Van Flein declined to say exactly when or where the interviews will be held, only that they will occur later in the week.
"I estimate each interview will take about three hours," he said.
Petumenos didn't immediately return a message left at his home Sunday.
An investigator for a separate probe by a legislative panel found earlier this month that Sarah Palin, the Republican vice presidential candidate, was within her right to fire Public Safety Commissioner Walter Monegan, an at-will employee.
But Stephen Branchflower, the Legislative Council's investigator, said Palin had violated ethics laws by trying to get her former brother-in-law, a state trooper, fired. Palin denies the charge.
She also said it was the Personnel Board's duty to investigate the claim, not the Legislature. The board hired Petumenos, an independent counsel, to conduct its investigation.
Last week, the Legislative Council voted unanimously to share with Petumenos confidential material gathered by Branchflower during that probe. The council published its findings but not the confidential matter.
The investigation was launched before Palin became the GOP vice presidential nominee, but has since taken on wider political implications.
Palin initially agreed to cooperate with the Legislature's investigation. But after she was tapped as John McCain's running mate, she said the probe had become too partisan and filed the ethics complaint against herself with the Personnel Board.
Democratic state Sen. Kim Elton, chairman of the Legislative Council, said last week it was important to share the confidential information to ensure that critical data was not segregated.
Under the Oct. 16 agreement, neither Petumenos nor the Personnel Board is allowed to reveal contents of the confidential documents without approval from the Legislative Council.
Despite Branchflower's findings, state lawmakers have no authority to sanction Palin for ethical misconduct. That's up to the three-member Personnel Board, which is appointed by the governor.
Two members of the board are holdovers from the previous governor and Palin reappointed the third. Members of the panel can be fired by the governor for cause.