ROCHESTER HILLS, Mich. — Authorities identified the man Sunday who opened fire at a splash pad in suburban Detroit before taking his own life, but his motives remained unknown as investigators worked to determine whether he left behind any hint of his plans.

Oakland County Sheriff’s spokesperson Stephen Huber said the shooter was Michael William Nash, 42, of Shelby Township. The gunman had no prior criminal history, but “it’s our understanding that he was undergoing some mental health challenges, but no one that we know of was notified,” Sheriff Mike Bouchard said during a news conference Saturday evening.

The splash pad shooting was one of at least four mass shootings that took place around the country Saturday night and early Sunday. Six people were shot in a residential neighborhood in Lathrup Village, another Detroit suburb. Seven people were shot at a party in Methuen, Massachusetts. Eight people were shot during a Juneteenth celebration in Round Rock, Texas; two people were killed in that shooting.

Authorities said Nash drove to suburban Rochester Hills on Saturday and opened fire at a splash pad in a city park around 5 p.m. A splash pad is a recreational area with a nonslip surface where people can play in fountains and water sprays.

The sheriff said Nash fired as many as 28 times, stopping several times to reload.

In the chaos, “people were falling, getting hit, trying to run,” Bouchard said. “Terrible things that unfortunately all of us in our law enforcement business have seen way too much.” The gunman was “apparently in no rush. Just calmly walked back to his car,” the sheriff said.

Nine people were injured, including an 8-year-old boy who was shot in the head; his 4-year-old brother, who was shot in the leg; and the boys’ mother, who was wounded in the abdomen and leg.

The 8-year-old and the mother were listed in critical condition Saturday evening; the 4-year-old was in stable condition. The six other victims, all at least 30 years old, were in stable condition on Saturday night. Huber, the sheriff’s spokesperson, said all the victims’ conditions were unchanged as of Sunday morning.

Nash eventually fled but apparently left his gun behind. Investigators were able to use the weapon’s registration information to track him back to the residence in Shelby Township he shared with his mother.

Deputies surrounded the home and eventually entered to find the suspect was dead. Bouchard said the man died of a self-inflicted gunshot wound.