COSTA MESA — A 32-year-old father unintentionally ran over and killed his 23-month-old son with his truck on the city's Westside, police said Monday.

Armando Medina went to move his 2007 Chevrolet Silverado, which was parked on the street, about 11:30 a.m. Sunday so that another car could pull out of his driveway, police said.

He did not know that his youngest son, Alexis Medina, was standing in front of the pickup when he drove forward, Costa Mesa police said.

Medina told investigating officers that he felt his vehicle "go over a bump," which he at first thought was just a speed bump in front of his duplex in the 600 block of West Wilson Street, according to a statement from the Police Department.

It wasn't until Medina heard neighbors screaming that he stopped to see what was going on, police said in a report.

The boy was taken to a local hospital, where he was pronounced dead on arrival due to massive head injuries, said Sgt. Phil Meyers.

Police have determined that neither drugs nor alcohol played a part in the accident. The investigation is ongoing.

"It's a tragedy no matter which way you slice it," Meyers said.

Meyers said "skilled investigators in the field" determined that fatality was the result of an accident.

"But we still have to review the reports and review the coroner's report and a whole myriad of issues before the case is closed," he added. "On its face, it appears to be an accident, but we still have to dot the I's and cross the T's and look into it thoroughly."

Meyers said the Medina family also has a 4-year-old, who was inside the pickup with his father at the time of the accident.

—Tom Ragan