Police in Maine said Saturday that the man who gunned down 18 people at a bar and a bowling alley and later took his own life, suffered serious mental health issues, but was able to buy weapons legally because he had never been forcibly committed to treatment.

The body of Robert Card, a 40-year-old army reservist, was discovered Friday night inside a tractor trailer near a recycling center where he used to work, said Maine public safety commissioner Mike Sauschuck. Card had shot himself.

Investigators are still struggling to determine Card's motive for carrying out Wednesday's massacre in the town of Lewiston.