A California woman is behind bars, on suspicion of homicide after her 4-month old baby died, and according to her boyfriend, she apparently laughed about it when he questioned her.

KTLA reports that authorities arrested Thi Nhat Ha Nguyen, 29, on Tuesday night at her residence. Officers responded to Nguyen’s Westminster home off of the 15000 block of Coronado Street a little before 11 p.m., where they found an unresponsive infant boy.

The little boy’s father, Hung Nguyen, said he noticed a mark across the baby’s face and when he questioned Nguyen, she “kept laughing.” When Hung tried to carry the baby, the infant wouldn’t move, which prompted the dad to call 911.

“I came in and said, ‘What’s going on?'” Hung told ABC7. “And she said, ‘Go!’ I came to get on the bed so I could touch my child. I see some marks … and my son he can’t move.”

Paramedics also arrived to the home and tried to revive the baby. They were unsuccessful and rushed the boy to the hospital, where he was pronounced dead.

So far, it’s unclear how or why the baby passed away, but Hung said it seemed like his son may have had head trauma. The official cause of death is pending a medical examiner’s autopsy results. Yet, based on the evidence and information found at the home, authorities arrested the mother.

“She loved him a lot,” Hung Nguyen said about the suspect. “I don’t think she did that. But who else?”

The Westminster Police Department Crimes Against Persons unit is currently investigating the case. The story is still developing. Check back with CrimeOnline as additional details become available.

[Feature Photo: Thi Nhat Ha Nguyen/Westminster Police Department]