Sacramento police say they have now made a pair of arrests in connection to Sunday’s mass shooting downtown.

On Monday, Sacramento police announced that Dandrae Martin, 26, had been arrested on charges of assault and illegal firearm possession. He is being characterized by police as a “related suspect.” His older brother, Smiley Martin was among the wounded at a local hospital. Police say he is under guard at the hospital, and was detained earlier today.

Police say detectives and SWAT have served search warrants at three residences in the area as part of the shooting investigation.

CBS News reports that police say investigators have received some 170 photos and videos through the online portal that was set up after the shooting. Detectives are now reviewing the evidence to determine charges. They noted that a stolen handgun used in the attack had been converted to a weapon capable of automatic fire.

Smiley Martin, 27, faces charges of possessing a firearm by a prohibited person and possession of a machine gun.

"Smiley Martin was located at the scene with serious injuries from gunfire and was transported to an area hospital for treatment," the Sacramento Police Department said in a statement.

Detectives have said they are looking for multiple possible suspects. No description of any suspects has been released.

The exact events that led up to the shooting are still under investigation, but at a press conference Sunday afternoon, police acknowledged the brawl just before the incident.

A total of six people were killed in the early Sunday morning shooting. A dozen others suffered varying degrees of injuries.