News 12 has learned that witnesses have been called to testify next week as Westchester County prosecutors pursue possible charges against scandalized real estate heir and convicted killer Robert Durst.

News 12 had previously confirmed that Westchester County prosecutors are pursuing charges against Durst for the disappearance of his first wife, Kathie, four decades ago. Now, News 12's senior investigative reporter Tara Rosenblum confirmed that several witnesses have already been called testify starting next Monday at the Westchester County Courthouse.

MORE: Buried Secrets: Robert Durst

It signals that it's likely a grand jury has been or will be empaneled by the end of this week.

News 12 first reported last Friday that District Attorney Mimi Rocah had made the decision to seek an indictment against Robert Durst in connection to the disappearance of his wife, Kathie McCormack Durst, in South Salem back in 1982.

Once heir to his family's billion-dollar real estate empire, the convicted killer is now behind bars in Los Angeles, where he is scheduled to be sentenced Thursday for the 2000 murder of his best friend, Susan Berman.

Prosecutors argued Durst killed her to stop Berman from implicating him in Kathie's case - which is being investigated as a murder.

News 12 has been told that several friends and relatives of Kathie are expected to be called as witnesses.

While none of them were available to react to these new developments, News 12's Tara Rosenblum says this is news they've been waiting for 40 years. In an earlier interview on News 12, one of Kathie's sisters talked about what the moment would mean to their longtime grieving family.

In another new twist this week, News 12 also learned the Manhattan District Attorney's Office is looking into allegations involving Durst's current wife, Debra Charatan.

Kathie's family attorney Bob Abrams has accused her of helping Durst cover up Kathie's murder, which is something Charatan's attorney has adamantly denied.

There was no comment tonight from the district attorneys in Westchester or Manhattan.

News 12 also reached out to Robert Durst's legal team three times and is still waiting for a response.