Pennsylvania ? A tractor-trailer slammed into a van carrying mentally disabled people on a trip to the Pittsburgh Zoo, flipping it onto its side, crushing it against a building and killing five people.

Witnesses told investigators the van stopped at an intersection and then pulled right in front of the semi on a rural highway. Crews worked for several hours Thursday to remove all the bodies from the van. Seven people were injured.

The accident happened about 9:45 a.m. in Somerset Township, about 30 miles south of Pittsburgh, minutes after the van had left a group home in Bentleyville.

“I just think it’s one of those terrible, sad freak accidents,” said Lynne Loresch, executive director of the Mental Health Association of Washington County, the group home operator.

Three residents of the group home and two staff members were killed. The six other people in the van – all residents – were taken to hospitals. The tractor-trailer driver was treated at a hospital and released.