Opinion by
Mr. Justice Eoberts,On the afternoon of January 31, 1967, appellant, a 19 year old youth, after having learned from friends that he was wanted by the police, voluntarily surrendered to the Scranton Police Department. Appellant’s action was motivated by the fact that he had been earlier advised that one Frank Smith, Jr., had been arrested for a series of burglaries, and had, shortly after being taken into custody, implicated appellant in the commission of these crimes. The following day (February 1, 1967) after having been detained and interrogated for over 21 hours, appellant signed a statement admitting his complicity in seven burglaries. Immediately thereafter, appellant was preliminarily arraigned.
On August 11, 1967, appellant pleaded guilty to one count of burglary (No. 20B), and was sentenced to 18 months imprisonment. On October 2, 1967, appellant proceeded to trial, before a jury, on the second burglary count (No. 7e), and was adjudged guilty. Prior to this trial, a timely filed motion to suppress the confession was denied. (At trial, this challenged confession was, over objection, introduced against appellant). Post-trial motions were denied, and appellant was sentenced to serve a term of 23 months imprisonment. On November 1, 1968, appellant pleaded guilty to the five remaining burglary charges then outstanding against bim (Nos. 7a, b, c, d, and 10). Appellant was sentenced on each of these offenses to serve a term of imprisonment of one and one-half to four years, each sentence to run concurrently with those already being served.
An appeal, allowed as if timely filed, was taken to the Superior Court, which affirmed in an opinionless per curiam order, with two judges dissenting. (Hoffman, J., filed a dissenting opinion, joined by Spaulding, *82J.). This Court granted allocatur, and we now reverse the conviction in No. 7e, and remand for an evidentiaryhearing in Nos. 7a, b, c, d, 10, and 20B.
Appellant here argues, as he did in the Superior Court, that the 24 hour “unnecessary delay” between his arrest and arraignment renders his confession, given only at the end of this period, inadmissible.1 Pa. R. *83Crim. P. 116(a) (effective January 1, 1965, replaced by Pa. R. Crim. P. 118 (effective May 1, 1970)); Commonwealth v. Dutton, 453 Pa. 547, 307 A.2d 238 (1973); Commonwealth v. Tingle, 451 Pa. 241, 301 A.2d 701 (1973); Commonwealth v. Futch, 447 Pa. 389, 290 A.2d 417 (1972). Appellant also contends that the hearing court’s erroneous refusal to suppress the confession was the primary motivation for appellant’s subsequent pleas of guilty to the remaining charges.2 Accordingly, appellant challenges the validity of these pleas. Cf. Commonwealth v. Walters, 431 Pa. 74, 244 A.2d 757 (1968); Commonwealth v. Stokes, 426 Pa. 265, 232 A.2d 193 (1967).
It is now well settled that at the time of appellant’s arrest (1967), all persons “arrested with or without a warrant” were required to “be taken without unnecessary delay before the proper issuing authority for a preliminary arraignment.” Pa. R. Crim. P. 116(a) (effective January 1, 1965) ; Dutton, supra. Where this mandate has gone unfulfilled by the Commonwealth, “all evidence obtained during ‘unnecessary delay’ except that which . . . has no reasonable relationship to the delay whatsoever” must be excluded.3 Futch, supra *84at 394, 290 A.2d at 419 (emphasis added). See Dutton, supra; Tingle, supra. Our task on appeal, therefore, is to determine whether there was an “unnecessary delay,” and if so, whether the evidence obtained is causally related to the delay. Our review of the instant record convinces us that both questions must be answered in the affirmative.
Here, the Commonwealth’s own evidence, as well as the opinion of the trial court, indicates that appellant voluntarily surrendered himself to the Scranton police on the afternoon (approximately 3:00 P.M.) of January 31, 1967. Appellant was thereafter detained and interrogated for 24 hours, and at 3:00 P.M. on February 1, 1967, finally signed a statement admitting his complicity in seven separate burglaries. During this 24 hour period, appellant was returned to his home, in the custody of the police, where evidence (cash receipts) of one crime was obtained by the authorities.
The Commonwealth does not in any way seek to justify this delay, but rather asserts that as appellant was not “threatened” or “abused,” his confession represents a knowing and voluntary, and therefore valid, act. However, this argument misses the point—Pa. R. Crim. P. 116(a) (as well as its progeny Pa. R. Crim. P. 118 and 116) requires that all arrestees be preliminarly arraigned “without unnecessary delay.” The Commonwealth has made no suggestion whatsoever that the instant delay was necessary.4 Accordingly, we must conclude that the 24 hour delay between appellant’s arrest *85and arraignment was “unnecessary,” and hence violative of Rule 116(a). Dutton, supra; Tingle, supra; Futch, supra.
Nor can it be seriously suggested that the challenged confession was not “reasonably related” to this “unnecessary delay.” Futch, supra at 394-96, 290 A.2d at 419. By the Commonwealth’s own concession, appellant, a 19 year-old youth with no prior police contact, did not “confess” until 24 hours after arrest and repeated interrogation.5 It was only then, after giving a written statement, that appellant was preliminarily arraigned. On these facts, “[w]e must conclude that the challenged statement here, as the evidence in Futch, supra, was ‘reasonably related’ to the ‘unnecessary delay’ and thus inadmissible.” Tingle, supra at 247, 301 A.2d at 704.
*86Having determined appellant’s confession to be invalid, and erroneously admitted at his trial, we are now called upon to pass on appellant’s contention that his guilty pleas to the six remaining burglary charges were primarily motivated by the illegally obtained confession. However, the record before us is insufficient to make such a determination. Accordingly, as no post-trial motions were filed by appellant prior to this appeal allowed as if timely filed, the record is remanded to the trial court for the filing of post-trial motions, with instructions, to the trial court, to conduct an evidentiary hearing. Cf. Commonwealth v. Starr, 450 Pa. 485, 301 A.2d 592 (1973); Commonwealth v. Kelly, 436 Pa. 21, 258 A.2d 325 (1969).
The judgment of sentence in No. 7e is reversed and a new trial granted. The records in Nos. 7a, 7b, 7c, 7d, 10, and 20B are remanded to the trial court for the filing of post-trial motions, with instructions to hold an appropriate evidentiary hearing.
Mr. Justice Eagen dissents.Although appellant did not raise this specific argument in his pretrial (1967) motion to suppress (which was based on purported violations of the standards set forth in Miranda v. Arizona, 384 U.S. 436, 86 S. Ct. 1602 (1966) and Escobedo v. Illinois, 378 U.S. 478, 84 S. Ct. 1758 (1964)), the Commonwealth has not objected to it being raised here, and we should not raise an objection sua sponte. Commonwealth v. Page & King, 451 Pa. 331, 334 n.3, 303 A.2d 215, 216 n.2a (1973). Indeed, had such an objection been voiced by the Commonwealth, it would have been without merit.
As Commonwealth v. Futch, 447 Pa. 389, 290 A.2d 417 (1972) (deciding for the first time in this Commonwealth 'that all evidence obtained during an “unnecessary delay” between arrest and arraignment, except that evidence unrelated to the delay, is inadmissible), was not decided until five years after appellant’s trial, appellant cannot be held to have waived the right to litigate that claim. As this Court made dear in Commonwealth v. Simon, 446 Pa. 215, 218, 285 A.2d 861, 862 (1971) (quoting from Commonwealth v. Cheeks, 429 Pa. 89, 239 A.2d 793 (1968) : “ ‘[I]t would be manifestly unfair to hold appeUant to a waiver when this waiver is alleged to have occurred at a time when neither the defendant nor his attorney had any way of knowing that there existed a right to be waived.’ Id. at 95, 239 A.2d at 796. Cheeks and its progeny . . . established the rule that failure to raise an issue in a prior proceeding is not a waiver when the legal principles upon which the issue is premised are newly announced in an appellate decision rendered subsequent to the date of the prior proceeding.” (footnote omitted). See also Commonwealth v. Jefferson, 423 Pa. 541, 546, 226 A.2d 765, 768 (1967).
Moreover, appellant’s present contention is properly before this Court for the additional reason that the “ground” for relief presented here is the identical one presented to the hearing court in appellant’s pretrial motion to suppress—the invalidity of the confession. Merely because appellant “advances a new or different theory as a basis for” relief, the ground or issue remains pre*83cisely the same. Commonwealth v. Slavik, 449 Pa. 424, 430, 297 A.2d 920, 923 (1972). Appellant here does not advance a new “ground,” he merely raises an argument legally different from that raised below. As this Court held in Slavik, supra (quoting from Sanders v. United States, 373 U.S. 1, 16, 83 S. Ct. 1068, 1077 (1963)), ‘“identical grounds may often he supported hy different legal arguments, . . .’ ” the “ground” appellant advances here, the invalidity of the confession, having been preserved below, is accordingly properly before this Court.
Appellant also challenges the plea entered in No. 20B, prior to the suppression hearing court’s refusal to suppress the challenged confession. Appellant alleges that this plea was also motivated primarily by the illegally obtained confession.
“This Court in Futch [447 Pa. 389, 393, 290 A.2d 417, 419 (1972) (citations omitted) (emphasis added)] made it clear ‘. . . *84that failure to comply with Rule 118 [and prior to 1970, Rule 116(a)] does not ipso facto render inadmissible evidence obtained by the police during the “unnecessary delay” and that it is incumbent upon defendant to show some prejudice from the delay.’ ” Commonwealth v. Tingle, 451 Pa. 241, 244-45, 301 A.2d 701, 702-03 (1973).
Chief Justice, then Judge Buboes, provided the following guidelines for determining “necessary delay” between arrest and *85arraignment: “Necessary delay can reasonably relate to time to administratively process an accused with booking, fingerprinting and other steps. . . .” Adams v. United States, 399 F.2d 574, 579 (D.C. Cir. 1968) (concurring opinion). See Commonwealth v. Tingle, 451 Pa. 241, 245, 301 A.2d 701, 703 (1973); Commonwealth v. Futch, 447 Pa. 389, 392, 290 A.2d 417, 418 (1972).
Although obviously disbelieved by the suppression court, appellant testified that: “After they had locked me up they came back and took me out again and kept asking me questions, and kept telling me that Frank had already confessed to certain crimes, and they named crimes that I never heard of, and then they took me back to the cell again and brought me back when I wouldn’t tell them nothing, and they said, ‘We are gomg to make it hard on you’, and things like that, ‘We are going easy on Smith’. Then they locked me up and after they had taken me out of my cell and took me back. As they would be locked me up they would be bringing Smith back in again and bringing him out and later on coming and get me. The next day in the morning they came and got me and took me back again, and they told me they had Smith upstairs and he had signed a statement. ‘So you might as well do it too, we ioill go easy on you, and it won’t he so hard’, and things like that And when I told them I wasn’t going to they took me back and locked me up again.”