A 70-year-old man involved in a multi-vehicle crash died Thursday, apparently as a result of cardiac arrest brought on by the Wednesday evening collision, the CHP said.

Cecil Harry of Rohnert Park reportedly suffered minimal injuries as a direct result of the impact, but his heart stopped while he was still in his vehicle, and authorities are now investigating the incident as a fatal crash, CHP Officer Jon Sloat said.

The CHP said Harry was driving a Dodge Ram pickup in northbound traffic on Highway 101 when another motorist driving about 55 mph rear-ended him near Rohnert Park Expressway, propelling the Ram truck into and on top of a Chevy S-10 pickup.

Initial reports indicate the collision was caused by a solo motorist who abruptly switched out of the northbound carpool lane, immediately encountering slowed traffic ahead for which he was unprepared, the CHP said.

That driver, Santa Rosa resident Pedro Montef, 44, was driving a Chevy Silverado when it struck Harry's vehicle, causing a chain-reaction crash that also damaged a fourth vehicle, authorities said.

It remained unclear why Montef, who was traveling alone, was in the carpool lane during rush hour or whether he would be cited as a result.

A witness said his lane change was sudden, but he did not offer an explanation for his lane change, Sloat said.

Arriving emergency medical crews immediately had to begin CPR on Harry and continued life-saving techniques as he was rushed to Santa Rosa Memorial Hospital, Sloat said.

Harry was listed in critical condition early Thursday, a hospital spokeswoman said.

Sloat announced his death later in the afternoon.

The S-10 driver, Brian Cooper, 33, of Santa Rosa, somehow suffered only minor injuries and was released after treatment at Santa Rosa Memorial.

Harry's Dodge Ram "crushed the entire bed of the (S-10) truck, but it didn't quite get the cab," Sloat said.

Montef also was treated and released, hospital personnel said.

Authorities were still investigating the case and questioning witnesses, Sloat said.

You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com.