The former Texas judge who presided over Robert Durst’s 2003 acquittal in the grisly slaying of a rooming-house neighbor said she thinks he’s a serial killer — who also left a severed cat head on her doorstep.

Judge Susan Criss told “Inside Edition” that she found the dead kitty’s cranium after Durst was sprung from the slammer for dumping the dismembered remains of Morris Black into Galveston Bay and illegal gun possession in Pennsylvania.

“This was a perfectly clean and preserved cat head cut up by someone who knew what they were doing laying right there,” she said. When asked who she thought did it, Criss replied: “I strongly believe it was Robert Durst.”

Criss alluded to remarks made by Durst’s younger brother, Douglas, who last year told an interviewer that Robert had a “series” of seven Alaskan Malamute dogs, each named Igor, who “all died mysteriously, of different things, within six months of his owning them.”

“He practiced on those dogs, and that’s where he got some of those skills at cutting people up,” Criss said.

Criss also cited a 2001 jailhouse conversation between Durst and his wife, Debrah Lee Charatan, in which Durst was overheard describing how he once peeped through the windows of his brother’s home and using “Igor” as a code word for murder.

“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,’” Criss said.

Durst has long been suspected in the 1982 disappearance of his first wife, Kathie, and he was busted on Saturday in the 2000 murder of writer pal Susan Berman in Los Angeles.

At the time of her death, authorities who were reinvestigating Kathie’s disappearance wanted to interview Berman about the case, and Durst’s arrest came a day before he was heard on an HBO documentary whispering off-camera: “What the hell did I do? Killed them all, of course.”

Other evidence includes handwriting that links him to a note alerting cops to Berman’s “cadaver,” according to court records.

“I believe that Robert Durst is a serial killer,” Criss said.

Law enforcement sources on Thursday told The Post that additional evidence seized following Durst’s arrest Saturday at a New Orleans hotel could be “the icing on the cake” to convict him in Berman’s killing.

Cops found a mask, a loaded revolver with one spent round and about $42,000 in cash stashed in his room at the JW Marriott, according to court records.

A separate raid on a condo Durst owns in Houston also turned up a prepaid TracFone cellphone and several different SIM cards.

The TracFone is one of several “burner” cellphones that Durst has used since January, when authorities suspect he learned his phone was being tapped, sources said.