PONTIAC, MICH. -- Two of the nine people wounded in a weekend shooting at a suburban Detroit splash pad remain hospitalized in critical condition, including an eight-year-old boy who has “made amazing progress” after he was shot in the head, authorities said Monday.

The child's four-year-old brother was shot in the leg, and the boys’ mother was hit in the abdomen and leg during the random attack in Rochester Hills. The shooting was one of at least four mass shootings in the U.S. on Saturday and early Sunday.

“Reeling would be an understatement,” Oakland County Sheriff Mike Bouchard said of the boys’ father during a news conference.

Michael Nash, 42, fired as many as 36 times Saturday, stopping several times to reload, police said. He subsequently went home to Shelby Township, where he killed himself.

Nash had no criminal history but apparently suffered privately from “mental health challenges,” Bouchard said. He said investigators found at least 11 weapons inside the home, including the handgun they believe Nash used to kill himself. Bouchard said the gunman in 2015 legally purchased the 9 mm handgun used in the violence.

The sheriff said two of the people wounded have been released from the hospital. Another woman who had a wound to her forearm and back may be released later Monday, he said.

A splash pad is a recreational area with a nonslip surface where people can play in fountains and water sprays.

Bouchard said Nash had no connections to the splash pad or any victims. Investigators still have no information about the gunman's motive, and there is no indication anyone ever reported Nash's apparent mental health struggles, he said.

Nash’s neighbors told the Detroit News that his father died two years ago and that 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.

Elsewhere in the U.S., 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.

Rochester Hills is about 15 miles (24 kilometres) south of Oxford, where in 2021 a 15-year-old fatally shot four high school students.