MODESTO, Calif. (AP) – A Northern California man suspected of killing four children and two women has been charged with murder in one of the deaths.

The Stanislaus County district attorney’s office on Thursday charged 30-year-old Martin Martinez with murder and child endangerment in the October death of his girlfriend’s 2-year-old boy.

Martinez remained free until his arrest Sunday while the Modesto Police Department investigated.

The toddler died of head injuries suffered in fall while in Martinez’ care. Martinez told police the injuries were caused by an accident.

Martinez is also suspected of the Saturday killing of his girlfriend, their 6-month-old daughter, his girlfriend’s 6-year-old daughter, his mother and an unidentified 5-year-old girl.

Martinez remains jailed in Modesto, and it’s unclear whether he has retained a lawyer who could comment on the case.

MODESTO (KRON) – Martin Martinez, the prime suspect in the murder of his mother, former girlfriend, three children and a toddler was transferred overnight from Santa Clara County Jail to Stanislaus County, Modesto police said today.

Martinez is accused of killing his 6-month-old daughter; his ex-girlfriend 38-year-old Amanda Crews; his mother 57-year-old Anna Brown Romero; a 6-year-old girl, and a 5-year-old girl who is a distant relative, police Chief Galen Carroll said.

Officers responding to a request to conduct a welfare check on a Modesto home on July 18th discovered the bodies, Police spokeswoman Heather Graves said.

Crews was a beloved doctor for low-income patients at Scenic Faculty Medical Group, which is contracted to provide physician services at Stanislaus County clinics, according to county officials.MARTINEZ ARRESTED FOR KILLING 2-YEAR-OLD

“Our deepest condolences go out to the family, friends and patients of Dr. Crews. She was loved as a mentor to the residents she taught. She was loved as a physician by her patients and she was loved and respected by her colleagues,” the medical group and county said in a statement.

Martinez also faces murder charges in the death of Crews’ two-year-old son who suspiciously died in October of 2014.

The head injury that led to the death of 2-year-old Christopher Ripley in October of 2014 came just two days after the child was in Martinez’s care.

The warrant for Martinez’s arrest indicates that day care staff reported the young boy had previously suffered “three suspicious injuries” in and around the time he was being potty trained.

Martinez was booked into Santa Clara County Jail on Sunday and was transferred to Stanislaus County Jail late Wednesday night or early Thursday morning.

Modesto police have not disclosed a possible motive.