The volunteer, tasked with security for the march and later identified as Matt Alder, saw Gamboa assembling a legally owned, legally carried AR-15-style rifle near the march in downtown Salt Lake City on June 14. Alarmed, Alder called for another volunteer security guard before drawing a concealed handgun. As Gamboa tried to rejoin the march, Alder opened fire, hitting Gamboa and killing Ah Loo.

Immediately after the shooting, police arrested Gamboa on a murder charge. The arresting officer claimed that Gamboa’s actions had created the situation that caused Alder to fear for his life and the lives of others, prompting Alder to open fire.

As a result Gamboa was blamed for Ah Loo’s death for having “acted under circumstances that showed a depraved indifference to human life, knowingly engag[ing] in conduct that created a grave risk of death and ultimately caused the death of an innocent community member,” according to a police statement.

Gamboa was held without bail for five days under suspicion of committing a violent felony. Police briefly detained Alder but did not take him into custody.