Updated

ORANGE, Calif. -- A Southern California mother whose 7-month-old son was tossed from the fourth-floor of a parking structure was arrested and booked for investigation of attempted murder, police said Tuesday.

The infant remained in critical condition at University of California, Irvine, Medical Center, said Orange police Sgt. Dan Adams.

Sonia Hermosillo, 31, of La Habra, was arrested Monday night, hours after the baby was thrown over a parking structure railing at Children's Hospital of Orange County. It's believed the baby was thrown from the fourth floor of the structure, Adams said.

Hermosillo was being held without bail.

Detectives haven't speculated on a motive, Adams said.

A witness called 911 after seeing the baby falling just after 6 p.m. on Monday.

Surveillance video showed Hermosillo's tan Chevrolet Blazer sport utility vehicle with an empty child restraint seat leaving the parking structure a short time later, the sergeant said.

The female driver was the only person inside the SUV and the license plate was traced to the Hermosillo home.

During the investigation, Adams said the La Habra Police Department notified detectives that a man reported that his wife, Sonia Hermosillo, and their son were missing.

An Orange police officer driving past Children's Hospital at 10:15 p.m. spotted the Blazer, Adams said. The SUV was stopped and Hermosillo was detained for questioning, then arrested.