WOBURN, Mass. – A man accused of killing his wife, two children and mother-in-law in their suburban Boston home pleaded not guilty Friday as his lawyer said he may use an insanity defense.

Thomas Mortimer IV, who was brought into Woburn District Court wearing a bulletproof vest, was ordered held without bail.

Not-guilty pleas to four charges of first-degree murder were entered for Mortimer during his arraignment.

“It’s likely that mental health will be a live issue in this case,” defense attorney Denise Regan told Judge James Barretto.

Prosecutors released no new details during the brief proceeding.

They had said Thursday that Mortimer left two identical letters in the home that read: “I did these horrible things. What I’ve done was extremely selfish and cowardly. I murdered my family.”

Mortimer’s parents attended the hearing. “He’s a good kid,” his father, Thomas Mortimer III, of Avon, Conn., told reporters.

Barretto ordered Mortimer to undergo a mental health evaluation on Friday, and said his lawyer could be present for the evaluation.

District Attorney Gerard Leone has said the “brutal and unspeakable” slayings followed a fight and “ongoing marital discord.”

Mortimer was captured Thursday by police in northwestern Massachusetts. The day before, authorities were summoned to the family’s home in Winchester by a relative who could not reach them.

Inside the home, police officers found the bloodied body of Mortimer’s 41-year-old wife, Laura Stone Mortimer, and their son, Thomas Mortimer V, in the front hallway.

Not far away, the lifeless body of Mortimer’s mother-in-law, Ellen Stone, was under an oriental rug. Upstairs, at the end of a trail of blood, was the body of Mortimer’s 2-year-old daughter, Charlotte Mortimer, in her crib.

All appeared to have been killed by blunt trauma and sharp objects, prosecutors said.

Leone said there were signs Mortimer had attempted suicide before he fled the home, in an upper middle-class suburb north of Boston.

Leone said the slayings appeared to have taken place between late Monday and early Tuesday, the day Mortimer called in sick to work and called his son’s school to say he wouldn’t be in.

Mortimer had recently landed a job at M&R Consultants Corp., a Burlington technology consulting firm, after several months of unemployment, said Anil Shah, the company’s president.

Mortimer is due back in court on Aug. 10.