According to local news reports, all three victims were detainees. FBI Director Kash Patel confirmed no law enforcement officers were injured, and suggested he believed the motive was political:

While the investigation is ongoing, an initial review of the evidence shows an idealogical (sic.) motive behind this attack … One of the unspent shell casings recovered was engraved with the phrase ‘ANTI ICE.’

Huh, don’t know how to interpret that.