A South Bay woman faces a murder charge after confessing that she drowned her adopted son in a bathtub in their house, police said.

Tara McNeill Palajac allegedly killed the 12-year-old boy on Jan. 8 in a Conner Place residence. The 51-year-old Santa Clara woman, who has not yet entered a plea, initially reported that the child's death was an accident, authorities said.

Santa Clara firefighters and police officers responded to Palajac’s house, near Forest Avenue and Winchester Boulevard, after the woman reported finding her child unconscious earlier in the month.

Although he was rushed to an area hospital, the boy was pronounced dead roughly two hours after the incident, police said.

Palajac first claimed that she and the boy were at home when she discovered him floating in the bathtub water. However, she reneged on her story while being interrogated by detectives, according to the Santa Clara Police Department, which has forwarded the case to the District Attorney’s office.

"It's heart wrenching," neighbor Adriane Alston said. "We're a big city but small community feel so it's really tragic when someone that miserable and that bad off will do something like that to a child."

Police say the boy's death was not announced to the public because of the sensitive nature of the crime and the fact that the victim was a juvenile.

An investigation is ongoing and Palajac, who was charged with murder on Jan. 14, is slated to appear in court Feb. 1.

NBC Bay Area's Robert Handa contributed to this report.