HOULTON — The second phase of the trial of a man convicted of fatally stabbing a 10-year-old boy and two men in northern Maine got under way Tuesday with testimony about the defendant’s mental state.

Jurors in Superior Court convicted Thayne Orsmby of three murder counts on Friday. On Tuesday, following the state’s Patriots Day holiday, the defense began its effort to convince them that Ormsby was not criminally responsible because of his state of mind.

Ormsby, 23, is using an insanity defense in the killings of 55-year-old Jeffrey Ryan, Ryan’s son, Jesse, and a family friend, 30-year-old Jason Dehahn, at Ryan’s home in Amity on June 22, 2010.

Assistant Attorney General Andrew Benson told jurors Tuesday that it will be difficult for the defense to make a case of insanity because Ormsby admitted to police that he killed Dehahn and the younger Ryan to get rid of witnesses. Ormsby also destroyed evidence and fled to New Hampshire, where he was arrested on July 2, 2010.

“He was not even remotely psychotic,” Benson told the jurors.

The defense contends there’s more to the case. Ormsby sat stoically as one of his lawyers described the way his mother physically and mentally abused him as a boy.

His mother, Maria Ormsby, later testified that she abused drugs and alcohol through much of his childhood. Thayne Ormsby later went to live with an uncle, Steven Ormsby, who said his nephew saw a therapist for a time but eventually refused to continue therapy.

In Maine, murder carries a maximum penalty of life in prison. Those who are deemed not criminally responsible for their actions are committed to a psychiatric hospital.