Defendants Noreikis, Hibma, and Rothrock appeal from their convictions for attempting to manufacture a quantity of Dimethyltryptamine (DMT), a schedule I controlled substance, in violation of 21 U.S.C. § 846. Their principal contentions on this appeal relate to an alleged deficiency in the affidavit supporting the request for a search warrant and to alleged improprieties in the manner in which the search pursuant to the warrant was executed. The defendants also challenge the sufficiency of the evidence. The search and seizure issues *1178were raised at a pretrial hearing and the appropriate motions were denied by the district court without any findings of fact. The bench trial of the case followed immediately thereafter and a judgment of guilty was entered by the court, once again without findings of fact.1
Appellants first contend that the affidavit for search warrant executed by John T. Peoples, Special Agent, BNDD (Bureau of Narcotics and Dangerous Drugs), was insufficient to allow the magistrate to make an independent determination that probable cause existed to issue the warrant. The application itself consists of two affidavits. The first, part of which is a standard printed form, sets forth that 13 different chemicals (all in specified amounts) were to be found at 436 West 118th Street, Chicago, and that these chemicals “are precursors and reagents of a schedule 1(c) controlled drug and the possession of which is illegal pursuant to Title 21 U. S.C. 841(a)(1) & (2) when possessed with the intent to manufacture.” The second affidavit of Special Agent Peoples traces four of the chemicals — lithium aluminum hydride, methanol, acetone, and ethyl ether — into the house, detailing how the BNDD agents had knowledge that these chemicals were in fact in the house at 436 West 118th Street. The affidavit ends with the statement: “13. That the above described chemicals are known to your affiant as the essential precursors and reagents necessary to produce the Schedule I Controlled Substance Dimethyl - tryptamine.”
If the magistrate had relied only upon the second affidavit, the validity of the issuance of the warrant would have been questionable for three of the chemicals have substantial individual household uses — methanol, acetone, and ethyl ether —and the fourth, lithium aluminum hydride, although it might be a “red flag” which would merit suspicion, would not necessarily establish probable cause to believe illegal drugs were to be manufactured. United States v. Failla, 343 F.Supp. 831 (W.D.N.Y.1972). Although the agents were aware that the various chemicals were being purchased in a surreptitious manner, for some reason this fact was not adverted to in the affidavit. Cf. United States v. Moore, 452 F.2d 569 (6th Cir. 1971). However, the issue does not turn on the second affidavit alone for we have two affidavits which must be read in pari materia.
The purpose for requiring an affidavit for a warrant is to allow the magistrate to make an independent determination of whether there is probable cause to support the issuance of a warrant. The magistrate must be given the facts so that he can make an independent judgment and not rely on the mere conclusions of the officer. See Giordenello v. United States, 357 U.S. 480, 486, 78 S.Ct. 1245, 2 L.Ed.2d 1503 (1958). “[A] 11 data necessary to show probable cause for the issuance of a search warrant must be contained within the four corners of a written affidavit given under oath.” United States v. Anderson, 453 F.2d 174, 175 (9th Cir. 1971). Cf. United States v. Harris, 403 U.S. 573, 580-581, 91 S.Ct. 2075, 29 L.Ed.2d 723 (1971). We also must note, however, the admonition of the Supreme Court that “the courts should not invalidate the warrant by interpreting the affidavit in a hypertechnical, rather than a commonsense, manner. Although in a particular case it may not be easy to determine when an affidavit demonstrates the existence of probable cause, the resolution of doubtful or marginal cases in this area should be largely determined by the preference to be accorded to warrants.” United States v. Ventresca, 380 *1179U.S. 102, 109, 85 S.Ct. 741, 746, 13 L. Ed.2d 684 (1965).
When we read thq two affidavits together in a commonsense way, we agree with the result reached by the district court that the magistrate had a sufficient basis to find probable cause to support a search warrant. We reach this conclusion in part by analogy to the cases considering the sufficiency of affidavits which rely on tips from informers. In Aguilar v. Texas, 378 U.S. 108, 84 S. Ct. 1509, 12 L.Ed.2d 723 (1964), and Spinelli v. United States, 393 U.S. 410, 89 S.Ct. 584, 27 L.Ed.2d 637 (1969), the Court mandated a two-pronged test for such affidavits: the affidavit should set out, first, the underlying circumstances necessary to enable the magistrate independently to judge the validity of the informant’s conclusion that a crime was being committed, and, second, facts to support the above circumstances and show that they were credible and reliable. The first affidavit — in which the agent swore positively as to the presence of 13 chemicals on the premises of the house to be searched — satisfies the first prong of the test. A magistrate could conclude that one who had assembled or possessed those chemicals was in fact doing so with the intent to manufacture a controlled substance even though it did not include ' every essential chemical.2 The second, and more detailed, affidavit then serves to meet the second prong of the test. It reflects the basis for the government agent’s knowledge that some of the chemicals were on the premises, thus providing facts to support the credibility and reliability of the first affidavit. That the second affidavit traces into the house only four of the thirteen chemical agents named in the first affidavit does not make it insufficient. The government need not, in its affidavit, corroborate every detail, but there should be at least a representative number of the details in order to give suitable reliability for a warrant to issue. Here there was.
The agent was not relying on an informant’s tip but rather on the investigative work of the BNDD agents when he swore that certain chemicals were on the premises; the corroborative background as to how this knowledge was obtained is necessary in such measure as to give the magistrate confidence in the reliability of the first affidavit. The situation is comparable to the revelation of past instances of reliable tips by an informant to demonstrate that his present tip should be credited. While upholding the issuance of the warrant in this case, we must also observe that better practice would be to err on the side of as much specificity as possible to avoid the possibility of a successful subsequent suppression attempt.
Appellants raise a second, and equally serious, challenge to the admission of the evidence seized at Hibma’s house. Appellants contend that in executing the search warrant the agents violated 18 U.S.C. § 3109,3 in that they did not announce their purpose or authority nor did they wait until “refused admittance” before breaking open the doors to the house. The Supreme Court has held in Miller v. United States, 357 U.S. 301, 78 S.Ct. 1190, 2 L.Ed.2d 1332 (1958), and Sabbath v. United States, 391 U.S. 585, 88 S.Ct. 1755, 20 L.Ed.2d 828 (1968), that failure to comply with 18 U.S.C. § 3109 compels suppression of any evidence seized during the search. In both Miller and Sabbath the Court *1180emphasized that 18 U.S.C. § 3109 was merely the codification of the common law rule which required officers of the law to give notice of both their authority and their purpose before forcing entry to a man’s home. Procedures smacking of Gestapo tactics should have no place within the American system of law enforcement. There is no claim of “exigent circumstances” in the present case but the question is solely whether there was sufficient compliance with the statute to negate suppression.
The testimony on this issue at the pretrial hearing was somewhat contradictory. The appellants attempt to cast doubt upon the testimony of some of the agents as to what they did or did not do; however, we must look at the evidence in the light most favorable to the government, leaving the determination of credibility to the district court.
The Hibmas arrived home at approximately 11:30 p. m. At approximately the same time, if not somewhat before, Agent Peoples arrived with the search warrant. The house itself had been under surveillance since at least 6 p. m. that day. There were 14 persons in the raiding party, 3 of whom were government chemists who were to examine the evidence seized. After the Hibmas entered the house, the agents waited and, when the house was completely dark at about midnight, they split into groups and at a prearranged time began to knock at each of the house’s three doors. At trial both sides seem to have agreed that the front door was the first one broken open. As to that door, Agent Skaggs testified that he thought he heard movement inside before he knocked and that he definitely heard a dog running and barking inside after he knocked. He stated that he was unable to find the doorbell and so knocked loudly, at the same time announcing his authority and purpose. He then knocked again and repeated his announcement. After waiting about 30 seconds without hearing any response, he kicked the door in. During the time he was knocking, he was unable to hear any other agents knocking or announcing their authority and purpose.
The testimony of the other agents was similar to that of Agent Skaggs, except that it appears that Agent Thompson, who was assigned to the basement door, waited approximately a minute and a half to two minutes before he broke in the door.
Both Hillary and George Hibma testified that they did not hear any knocking or announcements. In fact, they were both in bed when they heard the dog bark. Appellant Hibma then went to look at the front door and when he saw the people congregated outside his front door he started to return to the bedroom to put on some clothes. At this point the door was kicked in.
We have no way of knowing whether the district court gave any credence to the testimony of Hibma and his wife; however, for the purpose of this appeal we must take it that the agents did announce their authority and purpose. Thus, United States v. Likas, 448 F.2d 607 (7th Cir. 1971), is clearly distinguishable. The real issue involved in this appeal is whether or not they had been legally “refused admittance” before they forced open the doors.
It is not necessary that the agents wait until the occupants of a house have affirmatively or articulately refused them entrance before they can break in. “Such refusal is present where it can reasonably be inferred from the actions or inaction of the occupants of the premises to be searched.” United States v. Augello, 368 F.2d 692, 694 (3d Cir. 1966), vacated on other grounds, 390 U.S. 200, 88 S.Ct. 900, 19 L.Ed.2d 1036 (1968). In Augello, the federal officer knocked on the front door and announced his purpose, at which point the defendant’s sister went running toward the rear of the house yelling the appellant's name, the very person for whose arrest the officers had a warrant. The court found these facts sufficient to justify an inference of refusal of admission.
*1181The cases involving implied or inferred refusal based solely on failure of the occupants to respond to the announcement of authority and purpose provide less clear guidelines. The Second Circuit summarily approved breaking in after agents had waited a “minute or two, maybe more,” in United States v. Viale, 312 F.2d 595, 602 n.6 (2d Cir. 1963), cert. denied, 373 U.S. 903, 83 S.Ct. 1291, 10 L.Ed.2d 199. Judge Stevens set forth some aspects of the issue in United States v. Pratter, 465 F.2d 227, 230-231 (7th Cir. 1972):
“The statute applies to a critical situation which is fraught with danger for the entering officers as well as the occupants of the dwelling. Prompt action and surprise may be necessary to forestall escape, the destruction of evidence, or even violence; yet prompt action and surprise may also precipitate such consequences. In short, the execution of a warrant is a job for a professional, trained both to perform his mission and to heed the statutory command to show a decent respect for the privacy of the citizen before bursting into his home.” (Footnote omitted.)
Applying the above principles to the facts before us, it appears that the agents did not violate § 3109 when they forced open the doors to the Hibma house. We particularly note that both Hibmas had time to move about the house after the happening of what could reasonably be assumed was the knocking and announcing. The fact that Hibma chose to return to the bedroom in order to get dressed does not rebut the inference that the agents had waited a sufficient amount of time to allow someone to answer the knock if the occupants intended to answer it at all. We also note that other courts have upheld searches after the officers waited approximately a minute before forcing the door, e. g., United States v. Woodring, 444 F.2d 749, 751 (9th Cir. 1971).
Appellants emphasized on this appeal that many of the chemicals found in the Hibma basement had recognized legal uses. We may safely assume that if time had permitted the destruction of key chemicals,4 and destruction had in fact followed, the above contention as to the remaining innocuous ones would have been asserted here even more vigorously. One of the basic purposes, of course, for the law permitting this type of invasion is to avoid the possibility of the destruction of evidence of criminal activity.
Finally, appellants contend that even if the evidence was properly seized, the government failed to present sufficient evidence to show that the appellants had actually attempted to make the illegal substance. Appellants point to the lack of a power supply to run the pump as well as the fact that all of the chemicals were in a sealed and unopened condition.
In essence, appellants contend that at most they were only preparing to manufacture and that this is insufficient under the law to constitute an attempt to manufacture, with which they were charged in the indictment. While it seems to be well settled that mere preparation is not sufficient to constitute an attempt to commit a crime, 22 C.J.S. Criminal Law § 75(2)b, at 230 et seq., it seems equally clear that the semantical distinction between preparation and attempt is one incapable of being formulated in a hard and fast rule. The procuring of the instrument of the crime might be preparation in one factual situation and not in another. The matter is sometimes equated with the commission of an overt act, the “doing something directly moving toward, and bringing him nearer, the crime he intends to commit,” 22 C.J.S., supra at 231. “To manufacture” could for our present purposes be *1182reasonably defined as a process of combining ingredients to make a new product. The process could not occur unless the necessary ingredients were assembled. Arguably once the process of putting two ingredients together commenced there would be in existence a process of manufacturing even before the finished product emerged. In such event, it could be said that there was no longer an attempt to manufacture but an actual manufacturing. We do not need to decide, however, whether the finished product must have been realized for manufacturing as such to exist, for here, in our opinion, the steps went beyond mere preparation.
The testimony indicated that the chemicals in the basement were sufficient to synthesize DMT. As to the allegedly missing items of equipment, although a pump would have been useful for speeding the process and thereby obtaining a purer product, this was not deemed necessary.5 As to the lack of a source of heat, the appellants’ own expert witness testified that even a candle would be sufficient. Nor is the fact that no formula showing how to synthesize DMT was found on the premises sufficient to undercut the holding that an attempt to manufacture had legally materialized. This was not a situation of playing with a juvenile chemistry set. The preparations had progressed to the level of an attempt. See United States v. Coplon, 185 F.2d 629, 633 (2d Cir. 1950), cert. denied, 342 U.S. 920, 72 S. Ct. 362, 96 L.Ed. 688 (1952).
For the reasons hereinbefore set forth, the judgment of the district court is affirmed.
Affirmed.
. While special findings of fact are not required by Rule 23, Fed.R.Crim.P., in the absence of a request, their lack in the case of close or questionable determinations deprives an appellate court of knowledge of the basis on which the issue or issues were decided.
. Appellants also contend that the search warrant itself was insufficient because it failed to allege possession of any illegal drug. The chemicals specified were precursors of DMT and the allegations are sufficient under Rule 41(b)(2), Fed. R.Crim.P.
. 18 U.S.C. § 3109 provides :
“The officer may break open any outer or inner door or window of a house, or any part of a house, or anything therein, to execute a search warrant, if, after notice of his authority and purpose, he is refused admittance or when necessary to liberate himself or a person aiding him in the execution of the warrant.”
. For example, there was only one ounce of indole in the basement. A defense expert testified that this was an essential ingredient of DMT.
. Further, the evidentiary aspects of the lack of power for the pump is something less than clearly persuasive. This was developed on ci'oss-examination of a government forensic chemist who, when he was asked as to what type of power supply or source would be needed, replied, “I am not an expert, but it appears that it would need an electrical source of some sort because of the wires here.” He further said in response to a leading question that it would have to be some type of electrical source other than plugging it into a wall socket. We are left in the dark as to whether the pump required a heavier voltage than was available in the house or whether an item familiar to every householder, the heavy duty extension cord, could have been dropped down the basement stairway.