MENLO PARK (CBS SF) — The metal part that slammed through a car window on Highway 101 last week, killing an elderly driver, may have fallen off a Caltrans truck, state transportation officials said.

The revelation came during a California Highway Patrol investigation of Friday’s fatal accident and was confirmed over the weekend.

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“A California Highway Patrol preliminary investigation in coordination with Caltrans into Friday’s fatal accident has made an initial determination that the metal object that caused the accident may have come from a Caltrans water truck,” the state agency said in a statement. “The truck was driving between job sites at the time of the incident. Caltrans will continue to cooperate with CHP as they finish their investigation.”

The man, identified by the San Mateo County coroner’s office as Louis Schaefer of Mountain View, died after being struck in the neck by what appears to be a large metal screw-on nozzle cap that came off the back of a Caltrans water truck, Caltrans spokesman Myeast McCauley said.

It seems the nozzle cap came off the truck, which was traveling south in the far right lane near Willow Road, flew across several lanes of traffic and broke through Schaefer’s windshield as he was driving in the northbound fast lane.

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These kinds of caps are usually secured by a metal chain, McCauley said, and it’s still unclear how it got loose.

After being struck, Schaefer struck the center divider before eventually coming to a stop. No other vehicles were involved.

“Caltrans offers its deepest condolences to Mr. Schaefer’s family and friends,” McCauley said.

The CHP investigation into the death is still underway.

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