Exclusive: Judge Claims Robert Durst Left Cat Head on Doorstep And Killed Dogs For Practice

Plus, strange new brain surgery details.

Did Robert Durst practice murder by killing his own dogs?

That's the disturbing claim about Durst and his seven dogs that were all Malamutes and named Igor.

Judge Susan Criss presided at Durst's trial for shooting and dismembering his neighbor in Galveston, Texas, in 2003. He was acquitted. She believes Durst also dismembered his dogs.

She told INSIDE EDITION, "He had seven dogs and he named every one of them 'Igor' and they all came to some unnatural deaths. Some very bizarre unnatural deaths."

She also said, "He practiced on those dogs and that's where he got some of those skills at cutting people up."

In a recorded jailhouse conversation with his wife, Debrah Charatan in 2001, Durst even tells how he crept up to his estranged brother's home and peered through a window.

Judge Criss said, "While he was standing there he thought about 'doing an Igor.' And his wife tells him, Debrah tells him, 'Stop! Stop! Stop Bob! This is recorded.'"

Judge Criss said "Igor" was Durst's code-word for murder.

She told INSIDE EDITION that she believes she became one of Durst's targets.

After Durst's acquittal, she found something horrifying on her doorstep.

"This was a perfectly clean and preserved cat head cut up by someone who knew what they were doing laying right there," she said.

INSIDE EDITION's Diane McInerney asked, "Who do you believe left that at your doorstep?"

Judge Criss responded, "I strongly believe it was Robert Durst."

With Durst's arrest last weekend for the murder of his close friend, Susan Berman, cops across the nation are now checking everywhere Durst has lived and worked over the decades in an effort to link him to unsolved missing person cases.

Diane McInerney asked, "Do you believe he is a serial killer?"

Judge Criss responded, "I believe that Robert Durst is a serial killer."

Durst denies wrongdoing, but there are more clues that he was planning to flee to Cuba. Cops found wads of cash totaling $42,000 in his hotel room in New Orleans, plus a latex mask that came straight out of Mission: Impossible.

It's not just in the movies. INSIDE EDITION's Les Trent tried on one of the masks himself while covering the story of a guy who used one to rob a bank.

Meanwhile, there are reports Durst has had botox treatments and cosmetic surgery to subtly alter his appearance.

He also had brain surgery. Dr. Roshini Raj says the surgery may account for some of the bizarre behavior seen in his interviews for the HBO Documentary, The Jinx.

Dr. Raj told INSIDE EDITION, "When someone undergoes neurosurgery, there occasionally can be damage to certain nerves that effect the facial muscles and you may develop tics or twitches after it."