LEWISTON — A Mechanic Falls man accused of stabbing a neighbor last week killed two elderly women when he was a juvenile “because they’re weak,” a prosecutor said Wednesday.

Scott O’Donnell, now 50, was convicted in 1991 of two murders, Assistant District Attorney Katherine Hudson-MacRae said.

In one case, O’Donnell “beat and raped an elderly woman after he was helping carry her groceries,” using her cane as a weapon, Hudson-MacRae said.

He was a juvenile at the time, but was bound over as an adult and sentenced to 30 years in prison, she said.

While he was detained and awaiting the outcome of that charge, “he confided in a cellmate that he murdered another elderly woman by strangling her with a towel,” Hudson-MacRae said.

O’Donnell had “indicated that he chooses the elderly because they’re weak, and he fantasized about raping them,” Hudson-MacRae said.

At the time of the alleged stabbing last week, O’Donnell was on probation for the latter homicide case in which he was sentenced to 20 years in prison, with half of that time suspended.

Hudson-MacRae had filed a motion to revoke O’Donnell’s probation.

She said O’Donnell was seen on video stabbing the alleged victim with a knife. Possession of a dangerous weapon was a violation of his probation, she said.

He also appeared to be “terribly intoxicated that night,” another violation of the terms of his probation, Hudson-MacRae said.

Through his attorney, Justin Leary, O’Donnell denied Wednesday he violated the terms of his probation.

Eighth District Court Judge Susan Driscoll ordered O’Donnell held without bail pending a June hearing on the state’s motion to revoke his bail for violating his probation.

O’Donnell is accused of stabbing his neighbor at a mobile home park on Callahan Circle in Mechanic Falls the night of May 18, but claims his actions were self-defense.

He appeared Wednesday by videoconference from Androscoggin County Jail in Auburn.

O’Donnell is charged with two felonies: elevated aggravated assault and aggravated assault. The first is punishable by up to 30 years in prison; the second, by up to 10 years.

Leary said Wednesday his client was punched in the face by Ryan Muncey, which caused O’Donnell to assume a defensive posture. The two men had known each other from serving time in prison, Leary said.

O’Donnell’s fiancee, Kelly Ayer, told the judge Wednesday that O’Donnell had inadvertently driven on the lawn of his neighbor Muncey, 42, the day of the fight.

She said she and O’Donnell had been preparing for their wedding scheduled for three days later.

Due to his inexperience driving a manual transmission truck, O’Donnell drove onto Muncey’s lawn while trying to unload a pallet for a barbecue, she said.

O’Donnell apologized to Muncey, then got Ayer to move the truck from Muncey’s lawn, she said.

Later, Muncey’s wife/girlfriend came over to O’Donnell’s home and banged on his door, “being confrontational with me about the grass,” Ayer said.

She told the woman O’Donnell would resolve the issue with Muncey, but was yelled at by the woman, who stood at her door and called her epithets, Ayer said.

“She came in my house looking for a fight,” Ayer said of the woman. “They came to our house looking for a fight four times that night,” she said of the couple.

“All we’re trying to do is live a peaceful life,” she said, saying O’Donnell “is not violent” and has not been in any trouble since he was released from prison.

Since he has been on probation for the past four-and-a-half years, O’Donnell has “faithfully reported” to his probation officer, completed his counseling and works full-time, Leary said.

“He’s done everything you could hope for and more for a probationer,” Leary said.

He said police were called repeatedly to the scene by a neighbor who was complaining about Muncey, not O’Donnell.

A judge last week had set O’Donnell’s bail at $12,500 cash on the new charges, but he will remain in jail until his probation revocation hearing next month.