Police on Sunday were trying to determine who was driving a stolen truck loaded with illegal immigrants that smashed into other vehicles Saturday and rolled over, killing six people and injuring 15, some critically.

Immigration and Customs Enforcement officials questioned a man they had believed was the driver, but he turned out to be a passenger, said Arizona Department of Public Safety Sgt. Brian Preston.

Investigators said they think the pickup truck was traveling about 90 mph when it lost control at an intersection near Fort Huachuca, an Army post next to Sierra Vista in southeastern Arizona. Seventeen people were in the truck -- two women, 14 men and a boy, Preston said.

Deputies had been chasing the truck, but broke off pursuit before the accident.

Five people died at the scene of the 11-car crash Saturday, and one victim died later at a hospital. Of the 15 injured, one person was on life support and six were in critical but stable condition, Preston said.

James Lee, 74, and Emilia Lee, 71, of Huachuca City, were killed when the pickup hit their car and several others after swerving to avoid tire-damaging spikes placed on the road by police. The other four people who died were in the pickup; their names had not been released Sunday.