A US man who killed his 9-year-old son was reportedly in a dispute with the boy's mother about whether the child should be vaccinated.
Stephen O'Loughlin, 49, and his son, Pierce, were found dead in their San Francisco apartment last Wednesday.
Police are investigating whether the deaths were a murder-suicide and suspect he shot his own son before killing himself.
O'Loughlin's ex-wife Lesley Hu asked police to check on the apartment after hearing her son didn't show up to school that day.
The couple divorced in November 2016 and were involved in a nasty legal battle since July 2020, the San Francisco Chronicle reports.
Pierce's mother was seeking sole custody of Pierce which allowed her to make medical decisions such as getting vaccinated.
O'Loughlin, a known anti-vaxxer, had agreed to begin vaccinations on Tuesday, the day before his son was found dead.
But Hu's lawyer Lorie Nachlis told local news agency KRON4 he believed O'Loughlin killed Pierce to punish his mother.
"I think it is undeniable that Pierce's father suffered from an untreated mental illness which resulted in taking the life of his son and his own life," Nachlis told KRON4.
"He punished Leslie with the ultimate act of violence - killing her child, and she will suffer as I believe was intended for the rest of her life."
