After returning from a New Year's Eve party, the siblings were hanging out with a group of friends in the house they shared when someone pulled out a handgun to take pictures with, ABC 15 reported.
While posing alongside her brother, Manuel Ortiz, with the weapon, Savannah Ramirez accidentally shot him in the head at around 6 a.m. on Monday. Ortiz died instantly and family and friends wept as his body was carried out of the apartment.
Ramirez has been questioned and released pending further investigation, but Phoenix police Sgt. Steve Martos, said she would likely be charged with manslaughter if tests conclude there was alcohol in her system at the time of the incident.
Authorities are still investigating who owned the gun and whether or not the siblings were aware the weapon was loaded.
This was not the first time the siblings were seen posing with a weapon.
"On both Manuel and his sister's Facebook pages there are numerous shots of them posing with guns and making gang symbols," The Daily Mail reported.
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