VATICAN CITY, Sept 17 (Reuters) - The trial of Pope Benedict's former butler on charges of aggravated theft in the so-called "Vatileaks" scandal will start on September 29, the Vatican said on Monday.

Paolo Gabriele will be tried alongside Claudio Sciarpelletti, a Vatican computer expert, in a case which involved the leaking of sensitive documents alleging corruption in the Vatican.

Gabriele, who helped the pontiff dress, served him his meals and rode in the front seat of the popemobile at general audiences, is accused of taking letters from Benedict's desk and leaking them to reporters.

The episode, which has been highly embarrassing for the Vatican, exposed what some saw as a power struggle among some cardinals in the Vatican.

According to an indictment last August, Gabriele told investigators he had acted because he saw "evil and corruption everywhere in the Church" and wanted to help root it out "because the pope was not sufficiently informed".

Gabriele, who was arrested on May 23, faces up to six years in jail. Since the papal state has no prison, he would serve time in Italian jail unless the pope pardons him while Sciarpelletti is being tried on lesser charges of aiding and abetting. (Reporting by Philip Pullella; editing by Barry Moody and Jason Neely)