A man has been arrested on suspicion of fatally stabbing his co-worker's three-year-old daughter at their workplace in downtown Los Angeles.

The woman picked her daughter up from daycare and brought her to work at a garment factory on Monday.

When the woman stepped away from her work station, the Los Angeles Police Department says a co-worker began stabbing the girl without warning. The girl, known as “Baby Ruby,” died at a hospital.

Thirty-four-year-old Ricardo Augusto Utuy was arrested and booked on a murder charge. It's unclear if he has an attorney.

The motive is unclear.

Police Capt. Jorge Rodriguez tells the Los Angeles Times that witnesses reported the man would laugh and talk to himself. Witnesses tell KNBC-TV that the man was newly hired.