Prosecutor: Teen used hammer, knife to murder sister, mother and mother's boyfriend

(CBS/WCBS) QUINCY, Mass. - A prosecutor says the 18-year-old charged with murdering his mother, sister and mother's boyfriend in their Weymouth, Mass. home used a hammer and knife to commit the crime.

Donald Rudolph pleaded not guilty Monday to three counts of murder at his arraignment in Quincy District Court and was ordered held without bail, reports CBS station WCBS.

At the arraignment, prosecutor Craig Kowalski revealed new details about the slaying of Rudolph's 50-year-old mother Paula Rudolph, his 24-year-old sister Caylin, and his mother's boyfriend Frederick Medina, reports WCBS.

"Mr. Medina was found lying down on his back on the floor, his shirt soaked with blood, his throat was slit," said Kowalski.

Kowalski also said Medina had a stuffed animal in his mouth.

Police discovered the gruesome scene Thursday night. Rudolph, although not living at the home, was found at the scene with bloody hands.

Kowalski said Rudolph told officers when they asked why he had blood on his hands: "I'm (expletive). You'll see when you go in."

Police reportedly found a hammer and knife covered in blood wrapped in a placement on the kitchen table.

Rudolph's attorney said his client, who was ordered to undergo a psychiatric evaluation, has a history of mental illness and after his arrest Friday he did not know what had happened, WCBS reports.

At the time of the killings, Rudolph was on probation for shooting a BB gun at two women in Quincy earlier this year. The judge in that case gave him a suspended sentence.