John Lewis Hartley, 38, and his companion, Mercy Mary Becerra, 43, pleaded not guilty Friday to a murder charge, and each was held in jail in lieu of $2 million bail.
Deputy District Attorney Kurt Mechals said the defendants knew the victim's family but there doesn't appear to be a blood relationship between the child and the defendants.
The prosecutor declined to give a motive for the killing, saying the child -- who was about 2 years old -- died earlier this week, shortly before the defendants were detained as they tried to enter Mexico about noon Tuesday.
Mechals said the child died in a residential drowning, with contributing causes of malnutrition and dehydration.
“This is a young investigation,'' Mechals said outside court. “There's a lot of information that we're still gathering.''
Mechals said San Diego police investigated the case because the child's death came to light at the border.
He refused to give the child's name until her identity can be confirmed.
Judge Frederick Maguire scheduled a status conference for Aug. 18 at the South Bay Courthouse.
Hartley and Becerra each faces 25 years to life in prison if convicted.