Just this morning, the LA Times reports that investigators have arrested and charged Kareem Leiva, 32, the boyfriend of Heather Barron (10-year-old Anthony Avalos's mother):
...on suspicion of murder after he 'made statements' during an interview at the Lancaster station that led detectives to believe he was involved in the boy’s death.
Leiva is reported to have lived with the family on and off and had three children with Barron. He is currently being treated for a self-inflicted laceration to his upper chest and will be booked on a murder charge after he is medically clear, with bail set at $2 million. Barron was interviewed but has not yet been arrested.