JACKSON, MI – Michael Hamilton purchased a gun Aug. 8, 2012, his former girlfriend, Shannon Arquette, testified Thursday, Oct. 10.

"He bought it for protection in general," Arquette said during the fourth day of Hamilton's jury trial.

Hamilton, 34, is charged with open and attempted murder for allegedly shooting and killing Robert Marcyan, 49, and firing at Marcyan's twin brother, Richard, on Sept. 8, 2012, outside Hamilton's father's cottage on Wamplers Lake. Richard Marcyan was not hurt.

Michael Hamilton looks on with attorney George Lyons during opening arguments in his trial in front of Jackson County Circuit Judge John McBain on Monday, Oct. 7, 2013. Michael Hamilton is charged with open murder, assault with intent to murder and two counts of both using a firearm to commit a felony and automobile theft. If convicted of first-degree murder, he would go to prison for life.(J. Scott Park | MLIve.com)

George Lyons, Hamilton’s lawyer, is arguing Hamilton was involuntarily intoxicated by Adderall, prescribed to him to treat his attention deficit hyperactivity disorder, and the side effects of the drug rendered him insane at the time.

Arquette said Hamilton was hearing voices and acting paranoid. He would not let her open the windows and he was afraid “someone was going to get” Arquette and her 8-year-old son.

He could not sit and watch a movie, she said, answering questions posed by Lyons. “He would just be pacing all over the house, checking the doors, checking the windows.”

When Chief Assistant Prosecutor Kati Rezmierski cross-examined Arquette, she focused much on Hamilton’s drug use.

Intoxication from illegal drugs or alcohol is not a valid defense. Lyons has to show the intoxication was involuntary, meaning as a result of a prescribed, properly ingested medication.

Arquette said she and Hamilton smoked marijuana, and Hamilton had a problem with Vicodin, a prescription pain medication.

Answering further questions from Rezmierski, Arquette said she knew Hamilton had a friend with a heroin addiction. This was not a concern, she said. “Because they had been friends since childhood.”

Hamilton did not use heroin, she said, and when Lyons asked her more about the friend, she said he was on methadone, which treats narcotic addiction, and in therapy.

She said Hamilton had not taken Vicodin since he had some dental work done in May 2012. He smoked marijuana to help him eat and sleep, she said. She did not know if he had a medical marijuana card.

Before the shooting, Arquette last saw Hamilton on Sept. 5, 2012. The two lived together and she was cutting the grass. He told her to go inside and not to return to the yard.

She talked to him the Friday before Robert Marcyan died. He said he was at a cousin’s house. One of his cousins lives in a “dope house,” Arquette conceded.

“Michael had run out of money. He wanted me to bring him money,” she said.

He wanted her to take it to the cottage on Wamplers Heights Drive in Norvell Township.

It was late. She would have to drive a long distance, and she told him she would not. Hamilton was aggravated and hung up on her, Arquette said.

When with Hamilton, her boyfriend since December 2010, she said she never felt she was in any danger. He was "warm-hearted" and kind, she said.

It did not occur to her to have him “committed” when he started acting suspicious in the spring of 2012, she said, but she suggested he see his doctor. She thought he might have schizophrenia.

She had helped him find a doctor and he had begun seeing a psychiatrist in November 2011. The doctor then prescribed him Adderall.