NANAIMO, B.C. - A defence lawyer says the man accused of murdering two of his former co-workers at a British Columbia sawmill should be acquitted of first-degree murder and convicted of manslaughter.

In closing arguments at the B.C. Supreme Court trial in Nanaimo on Monday, John Gustafson told the jury there is little doubt Kevin Addison fired the weapon, but his actions were not premeditated or intentional, adding that his client suffered from depression that caused him to be "unthinking and unfocused."

Mill employees Fred McEachern and Michael Lunn died in the shooting on April 30, 2014, while Tony Sudar and Earl Kelly were shot but survived.

Addison, 49, a former Western Forest Products employee, was arrested at the mill office minutes after police received calls about an active shooter.

Gustafson told the jury that the question they must answer is what was going on in Addison's mind and if the evidence of his intention to kill has been proven beyond a reasonable doubt.

"What is in dispute is what was happening in Mr. Addison's mind," he said.

"Something was going wrong inside of his mind."

The trial earlier heard a witness describe Addison as in a zombie-like state when he shot and killed a man in the mill's parking lot and then went to the office to shoot three others, killing another man.

Addison is also charged with two counts of attempted murder.

Crown attorney Scott Van Alstine argued Addison intended the shootings and was motivated by revenge after being laid off from the mill in 2010.

"Mr. Addison was angry and frustrated because he was never taken back by Western Forest Products," he said.

"This dominated his thoughts and actions."

Van Alstine also questioned the defence's argument that Addison was depressed, saying: "If he was, as Mr. Gustafson described, he wouldn't be able to function in society, period."

In his opening argument earlier this month, Crown lawyer Nic Barber said Addison used a sawed-off shotgun to kill Lunn in the parking lot of the mill moments after he arrived at about 7 a.m.

Court has heard that Lunn, 62, was hit in the back of his right arm by a single blast, and that he died in the parking lot despite efforts by a security guard, a co-worker and paramedics to save him.

Barber said Addison then walked toward the company office and shot Sudar in the face before shooting Kelly and McEachern in the back.

The wounded McEachern, 53, hit Addison over the head with a chair but later died of his gunshot injuries, Barber said.

Barber told the court in his opening submission that during the shooting rampage, Addison yelled expletives and said: "You know who I am."