The deputy probation officer, a 32-year-old San Francisco woman, was driving east on Fairmont Drive near Foothill Boulevard at about 9:40 a.m. when she looked down, allowing her car to veer to the right, the CHP said.
The 1995 Honda Civic hit 56-year-old Timothy Bucher, who was also traveling east on Fairmont Drive on his bicycle. He hit his head on the car's windshield before landing in the roadway, according to the CHP.
Bucher was wearing his helmet but still suffered major injuries. He was taken to Eden Medical Center where he was pronounced dead, according to the CHP.
Castro Valley CHP spokesman Officer Daniel Jacowitz said investigations into fatalities typically take about 10 to 30 days.
The CHP is still inspecting the Honda and conducting interviews before investigators decide whether to ask the district attorney's office to press charges against the driver of the car, Jacowitz said.
Drugs and alcohol are not believed to have played a role in the crash, the CHP said. The woman was driving about 35 mph at the time of the collision.