Shotgun used to kill three children and a teacher at an Oregon school was a birthday gift from the gunman's mother

Shauntai Nickerson legally bought the Maverick 88 pump-action shotgun in August and gave it to her son, Griffin J. John II, 16, reportedly for recreational use. The former pupil blasted through doors at Silver Rail Elementary in Bend on Thursday. He killed Rhoam Summer, 5, an eight-year-old, an 11-year-old and teacher Megan Lambert, 25. Rhoam's parents have hired lawyers to probe how he got the gun.

According to court papers, John's father attacked his mother with a knife and beat her prior to his birth.

Parent Kaylub Giamanco, 36, followed the gunman inside and shot him dead.

Rhoam's parents say their son had planned to dress as a bunny for Halloween.