OPINION
ROBERTS, Justice.This appeal presents the issue of whether an accused not brought to trial as required by Pa.R.Crim.P. 1100 on charges arising out of a criminal transaction may, under Pa.R. Crim.P. 1100, be later brought to trial on other charges arising out of the same criminal transaction.1 We hold that he cannot.2
I
On July 28, 1974, appellant Leslie Earp was arrested and charged with murder, conspiracy, and several other offenses *372in connection with the shooting death of Robert Davis.3 On August 22, 1974, a certification hearing was held on all charges except murder. Appellant, who was sixteen years old at the time of arrest, was certified at the hearing as an adult on all charges.
At a preliminary hearing on the murder and conspiracy charges held on September 4, 1974, these charges were dismissed because of the Commonwealth’s failure to establish a prima facie case against appellant as required by Pa.R.Crim.P. 141(d). Despite dismissal of these charges, appellant was held continuously on the other offenses.
On February 4, 1975, a warrant was issued for the arrest of appellant for murder and conspiracy in connection with the same killing. Even though appellant since his arrest on July 28, 1974 had been continuously incarcerated, it was not until February 10, 1975, that appellant was arrested again. On April 16, 1975, 262 days after the first arrest, appellant filed a motion to dismiss all charges, contending that the Commonwealth had failed to comply with Pa.R.Crim.P. 1100. Rule 1100 requires the Commonwealth to bring a case to trial within 180 days of the filing of the criminal complaint against an accused. The calendar judge granted the motion except on the murder and conspiracy charges, reasoning that the arrest of February 10 on these two charges was the relevant date for measuring the Commonwealth’s compliance with Rule 1100 regarding these two charges. On August 11, 1975, 379 days after the first charges were filed, trial commenced, but ended in a mistrial. On December 8, 1975, a second trial began, and a jury found appellant guilty of murder of the first degree and conspiracy. Post-verdict motions, raising the Commonwealth’s failure to comply with Rule 1100, were denied, appellant was sentenced to life imprisonment, and this appeal followed.
II
Pa.R.Crim.P. 1100(a)(2) provides:
*373“Trial in a court case in which a written complaint is filed against the defendant after June 30,1974 shall commence no later than one hundred eighty (180) days from the date on which the complaint is filed.”
Rule 1100 was promulgated to protect not only the right of the accused to a speedy trial, but also the interest of society in the prompt disposition of criminal litigation. See Commonwealth v. Hamilton, 449 Pa. 297, 297 A.2d 127 (1972). As stated in the Commentary to the ABA Standards Relating to Speedy Trial:
“Speedy trial may be of concern to the defendant, as he may want to preserve the means of proving his defense, to avoid a long period of pre-trial imprisonment or conditional release, and to avoid a long period of anxiety and public suspicion arising out of the accusation. From the point of view of the public, a speedy trial is necessary to preserve the means of proving the charge, to maximize the deterrent effect of prosecution and conviction, and to avoid, in some cases, an extended period of pretrial freedom by the defendant during which time he may flee, commit other crimes, or intimidate witnesses.”
ABA Project on Minimum Standards for Criminal Justice, Standards Relating to Speedy Trial § 1.1 Commentary (Approved Draft, 1968). See Strunk v. United States, 412 U.S. 434, 93 S.Ct. 2260, 37 L.Ed.2d 56 (1973); Barker v. Wingo, 407 U.S. 514, 92 S.Ct. 2182, 33 L.Ed.2d 101 (1972).
Accordingly, we have held that Rule 1100(a)(2) “contemplates the commencement of the running of the mandatory period at the point criminal proceedings are initiated.” Commonwealth v. Mitchell, 472 Pa. 553, 559, 372 A.2d 826, 829 (1977). Moreover, our Rules provide that all charges arising out of a criminal transaction shall be treated as a single case:
“When more than one offense is alleged to have been committed by one person arising out of the same incident, the issuing authority shall accept only one complaint, and shall docket the matter as a single case.”
*374Pa.R.Crim.P. 131(b). Thus, Rule 1100(a)(2) and Rule 131(b) make clear that the 180 day speedy trial period set forth by Rule 1100 begins to run on all charges arising out of a criminal transaction upon the initiation of criminal proceedings charging the defendant with any offense arising out of that transaction.4
Rule 1100 recognizes exceptions to the requirement that trial be commenced within 180 days of the start of criminal proceedings. The Commonwealth is excused from the 180 day speedy trial rule if the length of time by which the Commonwealth exceeds the speedy trial period is attributable to delay caused by the unavailability of the defendant or defendant’s counsel, Pa.R.Crim.P. 1100(d)(1); Commonwealth v. Vaughn, 475 Pa. 227, 380 A.2d 326 (1977); Commonwealth v. Millhouse, 470 Pa. 512, 368 A.2d 1273 (1977), or defense continuances longer than thirty days, Pa.R.Crim.P. 1100(d)(2); Commonwealth v. Wade, 475 Pa. 399, 380 A.2d 782 (1977). The Rule allows for extension of the 180 day time period upon the application of the Commonwealth wherever trial cannot be timely commenced despite the due diligence of the Commonwealth, Pa.R.Crim.P. 1100(c); compare Commonwealth v. Shelton, 469 Pa. 8, 364 A.2d 694 (1976), with Commonwealth v. Mayfield, 469 Pa. 214, 364 A.2d 1345 (1976). These exceptions recognize that in some circumstances absolute insistence upon a 180 day limit would not promote the purposes of our Rule.
The Commonwealth does not argue that delay in the commencement of these proceedings was caused by unavailability of the defendant or counsel or by continuances granted the defense in excess of thirty days. Nor does the Commonwealth assert that it sought and was improperly denied a request for an extension. Instead, the Commonwealth contends that trial commenced within 180 days of criminal proceedings. The Commonwealth reasons that the relevant starting time for measuring the Commonwealth’s *375compliance with the Rule is February, 1975, when appellant while incarcerated was arrested again for the murder and conspiracy charges, and not July 28, 1974, when appellant was first charged with the offenses arising out of the shooting death of Robert Davis. We do not agree.
On July 28, 1974, appellant was charged with murder, criminal conspiracy, and several lesser offenses. These charges arose out of the same criminal transaction, the shooting death of Robert Davis. By charging appellant with these offenses, the Commonwealth initiated criminal proceedings against appellant, Commonwealth v. Mitchell, supra, and thus was obligated to bring these proceedings against appellant to trial within 180 days. Pa.R.Crim.P. 1100(a)(2); Pa.R.Crim.P. 131(b). Though charges of murder and conspiracy were dismissed at the preliminary hearing held September 4, 1974, other charges were still pending against appellant. Indeed, appellant remained in continuous custody on these charges. Though some of the criminal proceedings against appellant — the murder and conspiracy charges — were dismissed, appellant remained charged with possession of instruments of crime, possession of offensive weapons, aggravated assault, simple assault, and recklessly endangering another person. So long as a portion of the proceedings arising out of the shooting of Robert Davis remained pending, the Commonwealth’s obligation to bring these proceedings against appellant to trial within 180 days remained unaltered. Not having fulfilled this obligation, the Commonwealth has failed to comply with the requirements of Rule 1100.
The Commonwealth’s argument, if adopted, would allow the Commonwealth to grant itself in cases such as this an extension of the time for trial, without in any way reducing the burdens of the accused or the public. The accused, as here, remains incarcerated for long periods, subject to pretrial suspicion and uncertainty. Society must also wait for extended periods of time, postponing the orderly enforcement of the law, and jeopardizing the continued availability of valuable evidence. To allow such an extension without *376any justification by the Commonwealth would be inconsistent with our speedy trial rule. See Commonwealth v. Shelton, supra.
The result we reach is supported by the relevant provisions of the ABA Project on Minimum Standards for Criminal Justice, Standards Relating to Speedy Trial (Approved Draft, 1968). Section 2.2(a) of the Standards provides:
“ When time commences to run.
The time for trial should commence running, without demand from the defendant, as follows:
(a) from the date the charge is filed, except that if the defendant has been continuously held in custody or on bail or on recognizance until that date to answer for the same crime or a crime based on the same conduct or arising from the same criminal episode, then the time for trial should commence running from the date he was held to answer.”
See Dodge v. People, 178 Colo. 71, 495 P.2d 213 (1972) (quoting standard with approval). As the Commentary to this section explains, this section recommends an important qualification:
“The one important qualification in the standard is that the time is to be counted from the date the defendant was held to answer only if the offense later charged is ‘the same crime or a crime based on the same conduct or arising from the same criminal episode.’
“This qualification, which it is believed puts neither the defendant nor the prosecutor to an unfair advantage, is intended to clarify the significance of the fact that the offense charged may differ from the offense for which the defendant was held to answer. . . . The thrust of the qualification is that: (a) the prosecutor should not be responsible for the time which elapses before the charge was filed simply because the defendant was being held to answer on an unrelated offense; and (b) the defendant should not lose credit for the time which passes between the date he was held to answer and the date of the charge *377simply because the offense charged, arising out of the same conduct or episode, differs somewhat from the offense for which the defendant was held to answer.”
ABA Project on Minimum Standards for Criminal Justice, Standards Relating to Speedy Trial § 2.2(a) Commentary (Approved Draft, 1968).
Appellant was held in continuous custody on the other offenses for the entire period in which he could have been brought to trial. The dismissal of the murder and conspiracy charges did not relieve the Commonwealth of its obligation to bring the proceedings against appellant to trial, for charges arising out of the criminal transaction were still pending against appellant. The Commonwealth failed to bring appellant to trial within 180 days of July 28, 1974, has not justified the delay pursuant to Pa.R.Crim.P. 1100(d), and did not seek an extension of the time for trial pursuant to Pa.R.Crim.P. 1100(c). Appellant must therefore be discharged.
Judgment of sentence reversed and appellant ordered discharged.
EAGEN, C. J., concurs in the result. POMEROY, J., filed a dissenting opinion in which O’BRIEN and LARSEN, JJ., join. LARSEN, J., filed a dissenting opinion.. We hear this appeal pursuant to the Appellate Court Jurisdiction Act of 1970, Act of July 31, 1970, P.L. 673, art. II, § 202(1), 17 P.S. § 211.202(1) (Supp.1977).
. Appellant also asserts: (1) the verdict was against the evidence; (2) the verdict was against the weight of the evidence; (3) the homicide calendar judge erred in refusing to quash the murder and conspiracy indictments although they were returned at a time when a stay of all proceedings relating to appellant’s case was in effect; (4) Earp’s second trial violated his right not to be placed twice in jeopardy; (5) the suppression judge erred in denying appellant’s motion that all of the well pleaded facts in his two pre-trial applications to suppress evidence be deemed admitted because the Commonwealth failed to answer the applications within the time limits prescribed by Pa.R.Crim.P. 308(a); (6) the suppression judge erroneously held that appellant’s arrest on July 28, 1974, was supported by probable cause; (7) the suppression judge erred in refusing to suppress identification testimony of three Commonwealth witnesses; (8) the trial court erred in refusing to charge that the testimony of the Commonwealth’s alleged eyewitnesses be received with caution because these witnesses were young juveniles; and (9) the trial court erred in refusing to alter a portion of its charge relating to the testimony of a defense witness. Our disposition makes it unnecessary to reach any of these issues.
. The other offenses included possession of instruments of crime, possession of offensive weapons, aggravated assault, simple assault, and recklessly endangering another person.
. We need not decide the effect of a complete dismissal on all charges arising out of a criminal transaction upon the speedy trial rule.