Claudio Sciarpelletti has been accused of helping Paolo Gabriele leak the confidential documents while working in the Vatican’s Secretariat of State.
His lawyer argued that his client has no case to answer and the trial should be dropped.
Paolo Gabriele was given an 18-month prison sentence by the same court last month.
He admitted passing documents to a journalist, but said he did it out of love for the church and the Pope.
Paolo Gabriele is serving his sentence in a special detention room inside the Vatican’s police station, amid talk that he may be pardoned by Pope Benedict XVI.
Claudio Sciarpelletti, 48, handled secret communications in the Vatican’s Secretariat of State, the nerve centre of the Roman Catholic church.
His lawyer said an anonymous tip-off led Vatican police to search Claudio Sciarpelletti’s desk last May – finding an envelope addressed to Paolo Gabriele containing copies of sensitive documentation that had been leaked to the Italian media.
During his brief arrest, he is said to have given confused and contradictory explanations to investigators.
Defence lawyer Gianluca Benedetti denied the claims that the former butler and Claudio Sciarpelletti had been good friends, and said his client had been in an “emotional state” in his interviews with investigators.
The Vatican has since said he played a “marginal” role in the scandal.
Senior Vatican communications officer, Greg Burke, said that although Claudio Sciarpelletti was being charged with aiding and abetting Paolo Gabriele, it was “more like an obstruction charge” relating to his contradictory testimony, the Associated Press reports.
However, the judge refused Gianluca Benedetti’s request to drop the trial, and said the next hearing would be scheduled for Saturday. Analysts say his trial is likely to be shorter than Paolo Gabriele’s which lasted for a week.
Interest in the case centres on who the witnesses called to give evidence may be, correspondents say. A senior cleric and two top Vatican security officials are expected to be called, as well as Paolo Gabriele himself.
It is thought the trial may shine a light on the extent to which other Vatican employees, including clerics, may have been involved.
Much of the stolen information ended up in a best-selling book by journalist Gianluigi Nuzzi about corruption, scandals and infighting at the Vatican.
Paolo Gabriele confessed to taking the papers, but said he believed the Pope was being manipulated, and that he hoped to reveal alleged corruption at the Vatican.
The Vatican authorities have limited press access to Claudio Sciarpelletti’s trial and no TV cameras were allowed in court.
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