Dale S. Zenor was killed and five other people suffered minor injuries in the pileup at 4:20 p.m. Thursday in front of Acalanes High School at Stanley Boulevard and Pleasant Hill Road, Lafayette police said. No high school students were involved in the crash, and all those injured were adults, police said.

Police Chief Mike Fisher said preliminary reports indicate that a BMW heading west on Stanley at high speed rear-ended Zenor's Mazda convertible, causing a chain-reaction crash with four more vehicles. Zenor was killed when the Mazda flipped over.

"The BMW hit (the Mazda) so hard that it pushed it into a minivan in front of it," Fisher said "The impact forced the Mazda into the air and lightly to the left . . . so it's going up in the air and rolling. It rolls several times and then ends up in the northbound lane of Pleasant Hill Road."

The driver of the BMW, a 38-year-old Walnut Creek man, was treated at John Muir Medical Center and discharged. He was not cited, but may face criminal charges after police present their case to prosecutors.

"He's definitely the subject of the investigation," Fisher said.

E-mail Jim Zamora at jzamora@sfchronicle.com.