A man fatally shot his wife and their six children before he set the Michigan home they shared ablaze and turned the gun on himself, authorities said Monday.

Kristopher Karolkiewicz, 47, killed his wife, Amanda, 39, and their children, ages 5 to 15, Ottawa County Sheriff’s Capt. Jake Sparks said at a news conference.

They were found dead after first responders arrived at the home in Grand Haven, on the eastern shore of Lake Michigan, late Friday morning, Sparks said. Autopsies showed all had been shot, he said.

“The investigation at this point shows that this is a murder-suicide, with the fire being started after the murders,” Sparks said.

Four of the children were the couple’s biological kids, and two 11-year-old girls had been adopted, Sparks said, adding that the children’s identities would not be released at this time.

The Michigan State Police Fire Investigation Unit and a state police dog assisted the sheriff’s office with its investigation, State Police Lt. Pat Agema said by email.

Firefighters and police responded around 11:42 a.m. Friday after neighbors reported a house fire, Sparks said, and they found the bodies in different bedrooms.

“Preliminary indications are that the fire was intentionally set in numerous different places throughout the residence, in the interior of the home,” he said.

The violence may have started the night before and carried on into Friday morning, Sparks said, because there were earlier reports of the smell of smoke in the area.

Investigators believe Karolkiewicz used a registered handgun in the attack, Sparks said, but he wouldn’t say whether a firearm has been recovered from the fire-damaged residence.

Amanda Karolkiewicz was a substitute teacher, children’s book author and advocate for special needs children, NBC affiliate WDIV of Detroit reported.

“Our daughter Mandy was a kind and devoted soul who loved her family and her students,” her parents told WDIV. “We treasured every moment we had with her and her six children, and words cannot adequately express our devastation.”

Grand Haven Area Public Schools formally recognized Amanda this year as a dedicated substitute who “pours her heart into her work,” the station reported.

If you or someone you know is in crisis, call or text 988 or go to 988lifeline.org to reach the 988 Suicide & Crisis Lifeline or visit SpeakingOfSuicide.com/resources.