Authorities identified the man who opened fire at a splash pad in suburban Detroit before taking his own life, but his motives remain unknown as investigators work to determine if he left behind any hint of his plans.

Oakland County Sheriff spokesperson Stephen Huber said the shooter was 42-year-old Michael William Nash of Shelby Township. Sheriff Mike Bouchard said the gunman had no prior criminal history but apparently suffered privately from what the sheriff called “mental health challenges”.

“It’s our understanding that he was undergoing some mental health challenges, but no one that we know of was notified,” Bouchard said during an evening news conference.

The splash pad shooting was one of at least four mass shootings that took place around the US on Saturday night and early Sunday morning. Six people were shot in a residential neighborhood in Lathrup Village, another Detroit suburb. Seven people were shot at a party in Methuen, Massachusetts, and 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 5pm/ A splash pad is a recreational area with a non-slip 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 boy and the mother were both listed as being in a critical condition on Saturday evening. The 4-year-old was in a stable condition. The six other victims, all at least 30 years old, were in a 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 home in Shelby Township he shared with his mother. When police arrived, they found a car that matched the gunman’s vehicle.

Deputies surrounded the home and eventually entered to find the suspect dead. Bouchard said the man died of a self-inflicted gunshot wound. Deputies discovered a handgun next to the body and a semi-automatic rifle on the kitchen table. Bouchard said on Saturday Nash may have been planning a “second chapter” to the shooting.

An officer secures the scene of a shooting at the Brooklands Plaza Splash Pad. Photo / AP

Nash’s neighbours told the Detroit News Nash’s father died two years ago and he lived with his mother, who has been traveling the United States.

“He’s a loner. The blinds are always pulled over there,” neighbor Kyleen Duchene told the newspaper.

Nash’s mother was “super-friendly and nice” but Nash himself rarely left the house, neighbour Alex Roser said.

“And when he did, he didn’t even say ‘hi’ back to us when we would acknowledge him,” Roser said. “He was very quiet and didn’t want to be a part of our community.”

Bouchard said Nash had no connections to the splash pad or any of the victims. Investigators will try to determine if he left behind any writings and examine his electronic devices in the hope of shedding light on his motive.

“In terms of the ‘why’, I don’t know,” Bouchard said.

Rochester Hills is about 24km south of Oxford, where in 2021 a 15-year-old fatally shot four high school students. Saturday’s shooting came at the end of the first full week of summer vacation for students attending Rochester Community schools.

“I love my community and my heart breaks today,” Rochester Mayor Bryan Barnett said. “When I got on-scene, I started to cry because I know what a splash pad is supposed to be. It’s supposed to be a place where people gather, where families make memories, where people have fun.”

Bouchard called the attack “a gut punch” for the county.

“We’ve gone through so many tragedies,” the sheriff said. “We’re not even fully comprehending what happened at Oxford. And, you know, now we have another complete tragedy that we’re dealing with.”