A 20-year-old Arizona mother was arrested on suspicion of first-degree murder after her 2-year-old boy and 10-month-old girl were found dead in car seats, authorities said. Brittany Velasquez was charged with two counts of murder and was being held on a $2 million bond after police said they suspected foul play in the case.

The bodies of the baby and the toddler were found outside the family's home in Superior, a historic mining town of about 2,900 people about 60 miles east of Phoenix. Autopsies were being conducted to determine the causes of death of the children, whose names were not immediately made public.

Superior Interim Police Chief Christian Ensley said in a news conference Tuesday that the mother had first called authorities about the incident. Sheriff's spokeswoman Navideh Forghani, who was also part of the team that arrived at the crime scene, said it was unclear how the children were placed or left in the car. The motive of the killings also remains unknown.

However, there seemed to be a history of abuse as Ensley mentioned about the Department of Child Safety being involved with the family in early January after reports were filed concerning the well being of the two children. The state agency said Tuesday that it had received two calls about the children, including the one in January, but never found evidence of child neglect or abuse.

"The children showed no visible signs of abuse or neglect," the agency said in a response to a query from the Associated Press. "There were no legal grounds to remove the children from the parent's custody."

Giving some details of the family, Ensley said the children's father had died last year, and added that the incident was a "real blow" to the community.

Authorities said that when they arrived at the scene no one answered the door and that they later found the bodies of the children inside the car.