VISTA (CNS) - A judge ruled Monday that an Oceanside woman accused of intentionally drowning her toddler in a bathtub will go to trial. 

Veronica Rivas, 29, is charged with first-degree murder in the September death of her son, Elijah.

Rivas' mother testified at a preliminary hearing Monday. She said she was at Rivas' home on September 10 and went to find Elijah, intending to change his diaper. But when she picked him up from the bed, he was cold, wet and unresponsive.

"I took him outside with me and I was trying to pat him and when I got no response, that's when I called 911," she said.

Rivas was found unconscious in a separate area of the home.

The motive was unclear. Rivas and Elijah's father were estranged and amid a child custody battle.