A former secretary of ex-Israeli Prime Minister Ehud Olmert agreed to testify against him amid a plea bargain signed on Tuesday, Israeli media reported.

Shula Zaken, who had been Olmert confidant and right hand for more than a decade, agreed to testify against the former premier in a criminal corruption case known as the Holyland affair.

Zaken has been accused of taking part in the corruption affair. She will serve one year in jail as part of the plea bargain.

In the Holyland trial, Olmert is accused of expediting construction of a luxury residence complex while serving as Jerusalem's mayor from 1993 to 2003 and of other real estate ventures in exchange for bribes.

Zaken's cooperation with the prosecution may very well end up in a conviction against the former prime minister. She is expected to testify on the information she provided for Olmert regarding evidence against him in ongoing investigations, and also on money transfers that she helped take place between Olmert and contractors.

The judge might, however, paint her as an unreliable witness, considering that Zaken had changed her previous testimony.

Ehud Olmert served as Israel's prime minister between 2006 and 2009. He was forced to resign amid corruption allegations that started to surface against him in several cases.

The former premier was also indicted in two more cases of corruption and was acquitted.

Olmert was found not guilty in an affair in July. He was then suspected of receiving illegal donations of hundreds of thousands of US dollars in cash from Jewish American businessman Moris Talansky.

In the "Rishon Tours Affair" he was also acquitted from all charges, including double-billing reimbursement from public organizations on behalf of which he spoke abroad.

Olmert was, however, convicted in another case of irregularities during his tenure as Industry, Trade and Labor Minister between 2003 and 2005. He was accused of securing grants and tax breaks for a long-time colleague and close friend, attorney Uri Messer, and his clients.