Xuanhan Zhang, who turned 64 on Monday, was arrested and booked on suspicion of murder, according to the Los Angeles County Sheriff's Department. He was initially deemed a person of interest in the case.
The fire was reported shortly before 5 p.m. on Sunday in the 6000 block of Sultana Avenue, according to the L.A. County Fire Department. Firefighters had the flames out in less than half an hour, but ultimately found three bodies inside the residence.
An investigation is underway to determine how they died.
The two surviving victims - ages 64 and 68 - remain hospitalized in critical but stable condition. The names of the victims have not been released.
Zhang was interviewed on Sunday when he was considered a person of interest in the case. He is being held on $2 million bail and will be arraigned on Wednesday, authorities said.
Investigators say the suspect and the victims were all roommates.