Galveston police say Rebecca Rivera told them she drove to Galveston with her girlfriend and the body of her 4-year-old son and then tossed him into the Gulf of Mexico because he'd enjoyed visiting the beach and playing in the water, according to The Associated Press.
Known only as "Little Jacob" when he was first found eight months ago, police have since identified the boy as Jayden Alexander Lopez.
On Tuesday, Rivera and her girlfriend, Dania Amezquita-Gomez, were arrested and charged with fabricating or tampering with physical evidence.
According to court documents, Rivera admitted to police that she abused the boy because "she was stressed out and took this out on Jayden by striking him with 'whatever I could find.'"
The documents paint a grim picture of Jayden's final days.
His mother reportedly told authorities that Jayden bumped his head on a wall two weeks before his death and that his face began to swell.
In the ensuing days, Rivera said her son's condition deteriorated, according to the affidavit, and that in the hours following his death, she decided to take him to the seashore.
"The victim was a defenseless child," FBI agent Brian Gaines said at Wednesday's press conference announcing the arrests. "Jayden had no other advocate than us."