Former prime minister Ehud Olmert’s long-time top aide Shula Zaken reportedly provided police investigators Wednesday with substantive evidence tying her ex-boss to the massive corruption scandal known as the Holyland case.

Zaken produced a recorded conversation between herself and Olmert, in which the ex-prime minister can be heard instructing Zaken to commit actions that could be considered by the court as an obstruction of justice, her associates were quoted by Hebrew media as saying.

In the recordings, Olmert was said to urge Zaken not to sign a plea bargain with the prosecution, which offered her a reduced sentence in exchange for testimony against her former boss.

Israel’s Channel 10 news said it seemed likely that Olmert would be called in for police questioning over the allegation.

Prosecution attorneys must move quickly in order to decide whether to press additional charges against Olmert, as a verdict in the Holyland case is due on March 31, and district and state prosecutors must evaluate the new testimony by Thursday.

Zaken’s legal team was in talks with the prosecution several weeks ago to work out a plea bargain that would have seen her turn state’s witness in the case, in which Olmert (then mayor of Jerusalem) and others are accused of taking bribes to push through the Holyland project, a major residential development, a decade ago.

However, the prosecution said at the time that the testimony offered by Zaken wasn’t strong enough to justify a plea deal. The Justice Ministry said in a statement that the decision to decline her late testimony was made both because the trial had already passed the stage when new testimony could normally be admitted and because Zaken’s testimony could not be substantiated by “outside documentation.”

Former prime minister Ehud Olmert in Tel Aviv court as he prepares to give testimony at the Holyland trial, on Sunday September 29, 2013. (photo credit: Roni Schutzer/Flash90)

Former prime minister Ehud Olmert in Tel Aviv court as he prepares to give testimony at the Holyland trial, on Sunday September 29, 2013. (photo credit: Roni Schutzer/Flash90)

Olmert is “corrupt,” the long-time aide was quoted as having told police during questioning three weeks ago. She had voluntarily offered the testimony, which contradicted sworn evidence she has given over the years in several cases.

Zaken said that Olmert had put money given to him by the American Jewish businessman Morris Talansky to private use — to buy suits, pens, cigars and overseas holidays — rather than for political campaign funds. She also said Olmert knew all the details of an alleged double billing scheme for his various trips abroad, under which more than one organization would fund a trip, allowing the former prime minister to accrue funds which he used to finance family flights and upgrades to first class.

Olmert was acquitted of those allegations in 2012, and the state is currently appealing both verdicts.

The High Court of Justice rejected on Tuesday a petition by a nonprofit watchdog group to force the prosecution to allow Zaken to give last-minute testimony against Olmert. The Movement for Quality Government had appealed for Zaken to be accepted as a state’s witness against her former boss, but the High Court said the petition was lacking in factual justification.

Stuart Winer and Lazar Berman contributed to this report.