; or (2) issue a warrant and retake the parolee as provided in this section. (b) Issuance of summons or warrant (1) In general A summons or warrant issued under this section shall be issued by the Commission as soon as practicable after discovery of the alleged violation, except when delay is determined necessary. (2) Imprisonment Imprisonment in an institution shall not constitute grounds for delay of such issuance, except that, in the case of any parolee charged with a criminal offense, issuance of a summons or warrant may be suspended pending disposition of the charge. (c) Notice A summons or warrant issued under this section shall provide the parolee with written notice of— (1) the conditions of parole imposed under section 3638 that the parolee is alleged to have violated; (2) the rights of the parolee under this subchapter; and (3) the possible action which may be taken by the Commission. (d) Execution of warrants An officer of a Federal penal or correctional institution, or a Federal officer authorized to serve criminal process within the United States, to whom a warrant issued under this section is delivered, shall execute such warrant by taking such parolee and returning the parolee to the custody of the regional commissioner, or to the custody of the Attorney General, if the Commission shall so direct. 3643. Revocation of parole (a) Revocation generally (1) In general Except as provided in subsections (b) and (c)— (A) an alleged parole violator summoned or retaken under section 3642 shall be afforded the opportunity to have a preliminary hearing at or reasonably near the place of the alleged parole violation or arrest, without unnecessary delay, to determine if there is probable cause to believe that the parolee has violated a condition of parole; (B) upon a finding of probable cause, and except as provided in subparagraph (C)— (i) a digest shall be prepared by the Commission setting forth in writing the factors considered and the reasons for the decision