The mother of a defence contractor who gunned down 12 people at the Washington Navy Yard apologised on Wednesday on behalf of her son.

“To the families of the victims, I am so, so very sorry that this has happened. My heart is broken,” Cathleen Alexis said in a statement that she read from her Brooklyn, New York, home.

Her son Aaron Alexis opened fire Monday at the tightly guarded Washington Navy Yard, for which he had a valid entry pass, according to the FBI. He died in a shootout with police at the giant compound in the heart of the U.S. capital.

“Aaron is now in a place where he can no longer do harm to anyone, and for that am glad,” said Cathleen Alexis. “I don’t know why he did what he did, and I’m never going to be able to ask him why.”

Media reports have suggested that Alexis was delusional, but Pentagon officials could not confirm if he suffered mental health problems. Cathleen Alexis told CNN that she hasn’t been able to leave her home since Monday. — AFP