CAMARILLO, Calif.—Investigators used DNA evidence to track down and arrest a California woman accused of leaving her newborn baby to die in a strawberry field in May, authorities said Thursday.

Rosalba Cruz Moran, 20, was arrested last week on suspicion of murder in the death of the baby found by a field worker, Ventura County Sheriff's Sgt. Ian Laughlin said.

On May 21, the day the body was found, detectives collected more than 100 DNA samples from field workers in the area. Forensic scientists identified one donor as a close relative of the newborn's mother.

Moran was identified as the possible mother while she was already in custody on an immigration hold for a false documents charge, according to the Ventura County Star ( http://bit.ly/12J5joO).

DNA collected from Moran while in custody confirmed that she was the dead baby's mother. It's unknown who the father is.

Investigators don't have a possible motive.

"She is scared and has been held in custody for the better part of a month," said attorney Matt Bromund, who represents Moran on the false documents charge. "She is by no means a hardened criminal or a person who is used to this kind of situation."

Bromund added that Moran has no criminal history, was born in Mexico and worked at La Esperanza Farms in Camarillo—the farm where the baby was found. She is being held on $1 million bail.