WEST COVINA, Calif. -- A newborn boy was found in the toilet of a Subway restaurant Monday, and his mother, a homeless woman, was held by police who followed a blood trail, authorities said.

Mary Grace Trinidad, 38, was found behind a nearby auto parts store in the eastern Los Angeles suburb, police spokesman Rudy Lopez said.

Police were called to the Subway on South Azusa Avenue around 8:30 a.m. after a bleeding woman was seen leaving the sandwich shop and employees saw the blood trail came from the toilet, Lopez said.

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"Employees went inside and saw an umbilical cord hanging out of the toilet, then they found the baby in the toilet," Lopez told City News Service.

The crying infant was hospitalized in critical condition because being partially submerged in the cold toilet water lowered his core body temperature, police Lt. Dennis Patton told the Los Angeles Times.

Police followed the blood trail out of the Subway and found Trinidad, who also was taken to a hospital, police said.

A transient who is well-known in the neighborhood, she was wanted on a drug-related warrant and could face charges of attempted murder and child abandonment, police said.

"I've done this for 36 years. I thought I had seen everything," Lopez told the San Gabriel Valley Tribune. "I have no words to describe how I'm feeling about this."

CBS Los Angeles reported people in the area saw Trinidad walking up and down the strip for at least a day while in labor.

Under California's Safely Surrendered Baby Law, the parents or legal guardians of a newborn can turn in the child at a fire station or hospital with no questions asked if it is within three days of the birth and there are no signs of abuse.

CBS Los Angeles reported that the restaurant will remain temporarily closed while crews clean inside the building.