OPINION OF THE COURT
ADAMS, Circuit Judge.We are confronted in this case with the issue of the admissibility in a federal prosecution of evidence seized under the authority of a state search warrant, executed by city and federal law enforcement officers eight days after its issuance, despite the provision in the warrant to search defendant’s residence “forthwith.”
The district court held the warrant was stale when executed, and accordingly granted a motion to suppress evidence with respect to narcotics seized in the search of defendant’s own apartment. However, the court also held that the *653three ounces of heroin found in a trash area located on the ground floor of the apartment house were abandoned, and thus denied the motion in this respect. The jury found the defendant guilty of possession based upon . the evidence seized from the trash area, and this appeal followed.
I
The challenged search warrant was issued by a police magistrate to Detective Joseph Joiner of the Pittsburgh Police Bureau on August 27, 1973. Predicated on a probable violation of state narcotics laws, the warrant authorized the search of “1723 Fifth Avenue. Residence of Myrel [sic] Bedford and Mary Bedford (Mary Hughes),” and, in pre-printed form, provided that Detective Joiner was to conduct the search of the premises “forthwith.”
Eight days later, on September 4, 1973, Detective Joiner executed the warrant. He attributed the delay to his having been off duty for a few days during the intervening 3-day Labor Day weekend and for another day or so as a result of illness. After these periods of absence, he decided to wait for additional information as to when “the bulk of the narcotics” would be in defendant’s apartment. On the day of the search, the same informant whose earlier information had been used in establishing probable cause for issuance of the warrant, notified the police that the defendant was still in possession of narcotics. Soon thereafter Joiner executed the warrant. He was accompanied by seven other city police officers and four special agents of the Federal Drug Enforcement Administration. The special agents had been asked by Joiner, on the day of the search, to assist the local police officers in the execution of the warrant.
The Bedford residence was one of two apartments located on the top floor of a three-story, four-unit apartment house. Prior to searching the premises the officers executing the warrant established a surveillance of the immediate surrounding area and observed Bedford leave the building and drive away. Bedford was followed and stopped by some of the officers and taken back to the apartment house.
Upon arrival, Joiner notified Mary Hughes, who had been looking out of a third-floor window, that they had a warrant to search her apartment and asked her to open the outer door of the apartment building which was secured by a buzzer/lock system. She agreed, and about five minutes later appeared at the door and admitted the officers into the building. Most of the officers proceeded upstairs to search the Bedford-Hughes apartment, where a large quantity of heroin was seized.
One of the federal officers, Special Agent Maffett, remained on the ground floor to secure the entranceway. While there, Maffett was approached by a tenant of the building and asked to place a trash bag in the trash area located in the common hallway behind the stairwell on the ground floor. With the tenant’s permission, Maffett inspected this bag and found it contained refuse. He then deposited the bag in the trash area, where he examined other bags already left there. Search of the area and the bags resulted in the discovery by Maffett of three ounces of heroin and narcotics packaging paraphernalia.
The seized items were taken by the Pittsburgh police officers to be examined by local authorities for the purpose of establishing their contraband nature. Bedford was subsequently indicted by a state grand jury, but a pretrial motion to suppress was granted, and, inasmuch as the Commonwealth had no further evidence to present, an order was entered adjudicating him not guilty. Indictment by a federal grand jury followed, charging Bedford with a violation of the federal narcotics laws. See 21 U.S.C. § 841(a)(1).
II
When a warrant’s validity is being examined for federal prosecutory purposes and the resulting search is “state” in character, the warrant need *654only satisfy federal, constitutional requirements 1 rather than those of state law, which may involve stricter standards. Thus, even if the warrant did not comply with state law, evidence obtained from a subsequent search and seizure would not necessarily be inadmissible in a federal criminal trial. The test is whether the fourth amendment’s imperatives have been observed.2
(a) Particularity of the Warrant
Although neither party raised the issue of the warrant’s particularity, we deem it necessary to comment briefly on this point since a state court previously held the warrant to be constitutionally defective for its failure adequately to specify the place to be searched.
While it is not entirely clear whether the state court relied on federal or state law as authority for its holding, we are not, in any event, bound by its decision.3 “In determining whether there has been an unreasonable search and seizure by state officers, a federal court must make an independent inquiry, whether or not there has been such an inquiry by a state court, and irrespective of how any such inquiry may have turned out. The test is one of federal law, neither enlarged by what one state court may have countenanced, nor diminished by what another may have color-ably suppressed.” Elkins v. United States, 364 U.S. 206, 223-24, 80 S.Ct. 1437, 1447, 4 L.Ed.2d 1669 (1960).
Consonant with the fourth amendment’s dictate that warrants particularly describe the place to be searched, a search warrant directed *655against an apartment house will usually be held invalid if it fails to describe the particular apartment to be searched with sufficient definiteness to preclude a search of other units located in the building and occupied by innocent persons.4 However, “it is enough if the description is such that the officer with a search warrant can, with reasonable effort ascertain and identify the place intended.” Steele v. United States No. 1, 267 U.S. 498, 503, 45 S.Ct. 414, 416, 69 L.Ed. 757 (1925). “The standard . . is one of practical accuracy rather than technical nicety.” United States v. Gomez, 42 F.R.D. 347 (S.D.N.Y.1967). Accordingly, a warrant has been considered valid if it specifies the name of the occupant of the apartment against which it is directed, despite the absence of any physical description of the particular apartment.5
The warrant at hand fits this exception to the general rule, and therefore is valid under federal constitutional standards.6 It specified that the place to be searched was the “Residence of Myrel [sic] Bedford” located at “1723 Fifth Ave. being a 3 story brick dwelling.” Thus, reasonably construing the warrant, the search of the building was restricted to defendant’s residence.7
(b) Staleness of the Warrant
The element of time can admittedly affect the validity of a search warrant.8 Since it is upon allegation of presently existing facts that a warrant is issued, it is essential that it be executed promptly, “in order to lessen the possibility that the facts upon which probable cause was initially based do not become dissipated.”9 If the police were allowed to execute the warrant at leisure, the safeguard of judicial control over the search which the fourth amendment is intended to accomplish would be eviscerated. Thus, a search pursuant to a “stale” warrant is invalid.
It is generally accepted, however, that a warrant need only be executed within a reasonable time after its issuance, notwithstanding the presence of “forthwith” language in the warrant.10 Timeliness of execution should not be determined by means of a mechanical test with regard to the number of days from issuance, nor whether any cause for delay was per se reasonable or unreasonable. Rather it should be functionally measured in terms of whether probable cause still existed at the time the warrant was executed.11 “Only a probability of criminal activity is *656necessary for there to be probable cause,” United States v. Gimelstob, 475 F.2d 157, 160 (3d Cir.), cert. denied, 414 U.S. 828, 94 S.Ct. 49, 38 L.Ed.2d 62 (1973), and since the record reveals that there was continuing probable cause on the day of the search, execution of the warrant was reasonable.12
The district court below held that under either federal or state13 law the warrant was invalid because of an unreasonable delay in its execution. As a basis for holding the warrant stale under federal law, the district court noted the lack of any reasonable cause for the delay and also indicated that under Rule 41(c) of the Federal Rules of Criminal Procedure14 the execution of the warrant was improper. The court apparently did not consider whether there had been continuing probable cause as measured by federal constitutional law, which we believe is the appropriate inquiry under the facts presented.
In a number of cases involving prosecutions for federal narcotics offenses, courts have found that the initial probable cause which supported the issuance of the warrant continued tó exist at the time of the search, despite a delay in execution of the warrant.15 Under such circumstances, the element of judicial control is not undermined by delay, for as Judge Friendly has stated:
To permit agents to make the judgment that the averments of the affidavit are again satisfied, after a period of doubt, does not undercut the policy requiring an independent judicial determination of the existence of probable cause. The commissioner had already concluded that the facts recited in the affidavit were sufficient to establish probable cause. The determination that the facts on June 22 corresponded to the facts stated in the June 13 affidavit is one which the agents would have made even if they had returned to the commissioner to bring the affidavit up to date There is nothing to suggest that the heroin found on June 22 was not part of the same lot reasonably believed to have been on the premises on June 13. We thus find that the warrant was executed as soon as was reasonably possible . . . .16
*657In the case before us, there was nothing, other than the passage of the eight days during the period between the issuance and execution of the warrant, which altered the facts upon which the original affidavit was based and which gave the police probable cause to believe that the contraband specified in the warrant was in defendant’s apartment. Inasmuch as there was continuing probable cause at the time the search was conducted, the warrant was not unreasonably executed, and the defendant was not prejudiced by the delay.17
Since the warrant was validly executed, the search which followed was also valid and the conviction is therefore affirmed.18
. Whether a search conducted pursuant to a state warrant is characterized, in a federal prosecution, as “federal” or “state” depends upon the extent federal officers were involved in the search and seizure. Lustig v. United States, 338 U.S. 74, 69 S.Ct. 1372, 93 L.Ed. 1819 (1949); Byars v. United States, 273 U.S. 28, 47 S.Ct. 248, 71 L.Ed. 520 (1927). Each case will turn upon its own particular facts, but something more than “mere participation” by federal officers must be found before a state search is transformed into a federal undertaking. Id. at 32, 47 S.Ct. 248.
If the search_is_deemed “federal in character,” the legality of the search would be conditioned upon a finding that the warrant satisfied federal constitutional requirements and certain provisions of Fed.R.Crim.P. 41 “designed to protect the integrity of the federal courts or to govern the conduct of federal officers.” United States v. Sellers, 483 F.2d 37, 43 (5th Cir. 1973), cert. denied, 417 U.S. 908, 94 S.Ct. 2604, 41 L.Ed.2d 212 (1974). On the other hand, if the search is held to have been a “state” undertaking with minimal federal involvement, the warrant, assuming proper issuance under state law, need only conform to federal constitutional requirements. See, e. g., United States v. Johnson, 451 F.2d 1321, 1322 (4th Cir. 1971), cert. denied, 405 U.S. 1018, 92 S.Ct. 1298, 31 L.Ed.2d 480 (1972); United States v. Coronna, 420 F.2d 1091, 1092 n.2 (5th Cir. 1970); United States v. Cotham, 363 F.Supp. 851, 855 (W.D.Tex.1973) United States v. Grosso, 225 F.Supp. 161 (W.D.Pa. 1964).
An argument can be made that the search was “federal” in character, but we are more inclined to view the search as a “state” undertaking in which federal agents participated solely to supply additional manpower for the execution of the warrant. A number of facts support this position: (1) the warrant was issued under state law and directed to state officers; (2) the warrant was predicated on probable violation of state narcotics laws; (3) there was no evidence of bad faith on the part of either the state or federal officers; (4) federal agents did not assist in the obtaining of the warrant; (5) there was no evidence that federal agents instigated or supervised the search; (6) defendant was initially arrested by local police officers; (7) the majority of the evidence was found by local officers; and (8) the products of the search, placed in the custody of local police, formed the basis of a state prosecution.
. See United States v. Scolnick, 392 F.2d 320, 325-26 (3d Cir.), cert. denied, 392 U.S. 931, 88 S.Ct. 2283, 20 L.Ed.2d 1389 (1968). See also Elkins v. United States, 364 U.S. 206, 80 S.Ct. 1437, 4 L.Ed.2d 1669 (1960); United States v. Armocida, 515 F.2d 49 (3d Cir., 1975).
. It is a recognized principle that a federal court is not bound by a state court’s interpretation of federal laws or of a state statute under misapprehension of federal law. Furthermore, a state court may not impose greater restrictions, as a matter of federal constitutional law, on police activity with respect to search and seizures than the United States Supreme Court holds to be necessary, although it may interpret a feature of state constitutional law more restrictively than the Supreme Court has interpreted an equivalent provision of the Federal Constitution. Oregon v. Hass, 420 U.S. 714, 95 S.Ct. 1215, 43 L.Ed.2d 570 (1975).
. See, e. g., United States v. Higgins, 428 F.2d 232 (7th Cir. 1970).
. See, e. g., Moore v. United States, 149 U.S. App.D.C. 150, 461 F.2d 1236, 1238 (1972); United States v. Hinton, 219 F.2d 324, 326 (7th Cir. 1955); United States v. Barkouskas, 38 F.2d 837, 838 (M.D.Pa.1930).
. Whether the warrant is invalid under state standards for lack of specificity we need not consider. Apparently though, the state court judge, in granting Bedford’s motion to suppress evidence, was at least partially relying on an adequate and independent non-federal ground. See Commonwealth v. Copertino, 209 Pa.Super. 63, 224 A.2d 228 (1966).
. Although the scope of the warrant did not extend to a search of the trash area, if the police were lawfully inside the apartment building, they could search and seize items specified in the warrant and found in common areas of the building. Cf. United States v. Blake, 484 F.2d 50 (8th Cir. 1973), cert. denied, 417 U.S. 949, 94 S.Ct. 3076, 41 L.Ed.2d 669 (1974).
. United States ex rel. Beal v. Skaff, 418 F.2d 430, 433 (7th Cir. 1969).
. United States v. Nepstead, 424 F.2d 269, 271 (9th Cir.), cert. denied, 400 U.S. 848, 91 S.Ct. 50, 27 L.Ed.2d 86 (1970).
. See, e. g., United States v. Wilson, 491 F.2d 724 (6th Cir. 1974), and cases cited therein. These cases involved “federal” searches and application of Rule 41(c) of the Federal Rules of Criminal Procedure before it was amended, which required that searches be conducted “forthwith.” The courts eventually construed this directive in terms of reasonableness, mainly in an attempt to reconcile it with Rule 41(d) which specified that a warrant may be executed only within 10 days after its issuance.
. Cf. Sgro v. United States, 287 U.S. 206, 211, 53 S.Ct. 138, 77 L.Ed. 260 (1932). The dissent rejects the application of the continuing probable cause test to the facts of this case since it views the “forthwith” language as a purposeful, “judicial command that the warrant be served immediately.” However, the fact that *656the word “forthwith” is found in the pre-print-ed text of the state search warrant form is not dispositive of our consideration of the validity of the warrant and the legality of the search for federal prosecutorial purposes. For even though evidence may have been obtained unlawfully under state standards, it may be admissible in a federal prosecution if all federal standards are met. See note 2 supra.
. In United States ex rel. Beal v. Skaff, supra note 8, the court assessed the reasonableness of a state search conducted under authority of a state warrant, which commanded the police to search the premises “forthwith,” in terms of whether probable cause still existed at the time of execution. The court found there was continuing probable cause and that, therefore, the warrant and its execution were not viola-tive of the Federal Constitution. __
. State law is neither controlling nor even applicable here. See notes I and 2 supra.
. Inasmuch as we find the search to have been “state” in character, see note 1 supra, the validity of the warrant does not depend upon compliance with the Federal Rules of Criminal Procedure. But even if Rule 41(c) did apply, the warrant would not be invalid thereunder. The district court seems to have discounted, in effect, the 1972 amendment of Rule 41(c), which eliminated the requirement that searches be performed “forthwith,” and now requires only that the search be conducted within a specified period of time, not exceeding 10 days. While the warrant’s failure to specify a period of time for execution may, to a certain extent, dilute judicial control over the search and vest additional discretion in the executing officers, such failure would not by itself necessarily nullify a warrant if it is executed within 10 days and at a time when probable cause continues to exist. Cf. note 15 infra and accompanying test.
. See United States v. Wilson, supra note 10, at 725 (six-day delay); United States v. Rael, 467 F.2d 333, 336 (10th Cir. 1972), cert. denied, 410 U.S. 956, 93 S.Ct. 1429, 35 L.Ed.2d 690 . (1973) (five-day delay); United States v. Nepstead, supra note 9, at 271 (six-day delay); United States v. Dunnings, 425 F.2d 836, 840-41 (2d Cir. 1969), cert. denied, 397 U.S. 1002, 90 S.Ct. 1149, 25 L.Ed.2d 412 (1970) (nine-day delay).
. United States v. Dunnings, supra note 15, at 840-41.
. Even if the delay were held to be unreasonable, the evidence seized would not be inadmissible unless the defendant could “point to some definite legal prejudice attributable to this unjustified delay.” Spinelli v. United States, 382 F.2d 871, 886 (8th Cir. 1967), rev’d on other grounds, 393 U.S. 410, 89 S.Ct. 584, 21 L.Ed.2d 637 (1969). See also United States v. Cafero, 473 F.2d 489 (3d Cir. 1973), cert. denied, 417 U.S. 918, 94 S.Ct. 2622, 41 L.Ed.2d 223 (1974). “[I]f a prompt search would have disclosed nothing incriminating, and if during an unreasonable delay period the defendant brings incriminating evidence into or onto the premises which is seized as a result of the delayed search, the defendant has sustained legal prejudice.” United States v. McClard, 333 F.Supp. 158, 166 (E.D.Ark.1971), aff’d, 462 F.2d 488 (8th Cir.), cert.denied, 409 U.S. 988, 93 S.Ct. 345, 34 L.Ed.2d 255 (1972). On the record here, there is no basis for concluding that the contraband would not have been found if a search of the premises had been promptly conducted after issuance of the warrant.
. Because we dispose of this appeal on the ground that the warrant was not stale, it is unnecessary for us to consider the issues of abandonment, standing, and the effect of the police officers’ entry into the apartment building under color of a search warrant held to have been invalid by the district court.