Prince George's County police say it will take days to determine the cause of death of an 11-month-old girl whose mother was killed by a D.C. police officer, according to authorities.

Jaylin Wright was found inside an abandoned car late Thursday evening, shortly after the body of her mother, 20-year-old District Heights resident Wynetta Wright, was found by police in nearby Oxon Run Stream Valley Park. Both were pronounced dead at the scene.

D.C. police officer Richmond Phillips, 39, of the 2900 block of Oxon Park Street in Temple Hills, was charged with one count of first-degree murder for Wynetta's death, according to a police spokesman.

The medical examiner's office is still working to determine how Jaylin died, though Prince George's County Deputy Chief Gary Cunningham said it appeared she had been left in the car for days and may have died of heat exposure. If Phillips is found responsible for the young girl's death as well, he will likely be charged with a second count of first-degree murder.

Phillips had been issued a subpoena to appear in court on May 31 for a paternity hearing. Wright claimed that Phillips was Jaylin's father.

Cunningham declined to comment on the relationship between Phillips and Wright.

Wright and her daughter were reported missing to Baltimore County police on May 31. Prince George's County police took over the investigation once it was confirmed that the mother and child were last seen in Temple Hills, and issued a missing persons notice on Wednesday evening.

Phillips entered a District 4 precinct at an unspecified time, according to police, and was charged around 12:30 p.m. Friday.

According to D.C. police officials, Phillips has been an officer with the department since 2003, assigned to the 1st District. "This is a horrific crime, and our deepest sympathies go out to the Wright family," said D.C. Police Chief Cathy L. Lanier. "As we have seen all too often, domestic violence has its impact on the most innocent victims."

Phillips' mother, Ruth Harris, who lives with him in Temple Hills, said she didn't know anything about her son's relationship with Wright.

Phillips has been married to Ronda Nickie Phillips for 13 years, according to Harris, and they have a 12-year-old daughter, Ayame. He was a good son and father, she said, and a computer whiz at the police department.

Wright had an interest in law enforcement, officials said. She was a member of the Prince George's County Sheriff's Office explorer's program, which gives young people leadership experience and training in law enforcement, since 2009, and had been promoted to private first class.