The Latest on two teen siblings killed in a shooting started by an argument over a T-shirt (all times local):

11:45 a.m.

Authorities say a man accused of fatally shooting a teenage brother and sister during an argument started over a T-shirt may have been a stepfather figure who was romantically involved with the victims' mother.

Salt Lake County Sheriff Jim Winder said Friday investigators are working to confirm the exact nature of a long-standing relationship between 28-year-old Mario Cervantes-Angel and the victims.

Cervantes-Angel was arrested on suspicion of two counts of aggravated murder, a charge that carries the possibility of the death penalty.

No attorney was immediately listed for Cervantes-Angel in court records, and a search of public records showed no listed phone number.

Police say Cervantes-Angel fired several shots after 16-year-old Jose Izazaga came out with a knife to defend his sister because she was being pushed around. The fight started after another man accused 15-year-old Abril Izazaga of taking a shirt late Wednesday.

The man who started the argument turned himself into to police. Winder said he has been released and has not been charged with any crime.

9:45 a.m.

A Utah man accused of killing a teenage brother and sister in what's being called a senseless slaying over a T-shirt has been arrested on allegations that could become a capital murder case, authorities said Friday.

Police say the 28-year-old Mario Cervantes-Angel fired several shots after 16-year-old Jose Izazaga came out with a knife to defend his sister because she was being pushed around. The fight started after another man accused 15-year-old Abril Izazaga of taking a shirt late Wednesday.

The girl died at the apartment complex in the Salt Lake City suburb of Midvale, and her brother died at a hospital shortly after.

The man who originally started the argument turned himself into to police, but hasn't yet been formally arrested and his name hasn't been released.

No attorney was immediately listed Cervantes-Angel in court records, and a search of public records showed no listed phone number.