The teenage victims of a deadly stabbing at a McDonald's restaurant in southwestern Japan last weekend are not believed to have been specifically targeted, an investigative source said Wednesday.

Given there were no reports of previous disturbances at the fast-food restaurant in Kitakyushu, Fukuoka Prefecture, nor any instances of conflict involving the two junior high school students, one who was killed and the other seriously injured, the police suspect it was not a targeted attack, the source said.

The assailant, described by witnesses as a man around 40 years old, remains at large after the attack that occurred around 8:25 p.m. Saturday and left Saaya Nakashima, 15, dead and a yet unnamed 15-year-old male seriously injured.

The man spent less than 30 seconds in the store, stabbing each victim once, before fleeing on foot.

The male student was quoted as saying he and his acquaintance were "stabbed by a complete stranger."

The restaurant was open on Wednesday, but only for drive-through orders, with police cars frequently patrolling the area.