Smiley Martin, 27, faces charges on suspicion of being a prohibited person in possession of a firearm and possessing a machine gun.
Martin was hospitalized with serious injuries after he was shot at the scene of the shooting on K and 10th streets, police said.
He has been under the supervision of officers. Once he is discharged from the hospital, the police department said he will be booked into the Sacramento County Main Jail.
Martin’s 26-year-old brother Dandrae has already been arrested as a “related suspect.” He faces felony charges on suspicion of assault with a deadly weapon and being a convicted person carrying a loaded firearm.
“This individual has not been arrested for any homicide related to this incident. The investigation is highly complex involving many witnesses, videos of numerous types and significant physical evidence. This is an ongoing investigation and we anticipate more arrests in this case,” Sacramento County District Attorney Anne Marie Schubert said of Dandrae Martin’s arrest.
Eighteen victims were wounded early Sunday morning, sparking chaos in an area of downtown known for its nightclubs and entertainment scene. Six people died.
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At the scene, investigators said they found over 100 shell casings and a stolen handgun that had been converted into an automatic firearm.
SWAT team members and detectives have since served search warrants at three homes.
The Sacramento Police Department is gathering video and photo files from witnesses through its evidence portal. A QR code was also created for people who may have captured the mass shooting on their smartphones.