When he learned police were looking for him, Scott Johnson tried to assure his mother that he would take care of the situation.

"He walked out, and that's the last time I saw my boy," Judy Johnson said.

The next morning, her son emerged from woods in northern Wisconsin and surrendered to police who suspect he gunned down a group of young swimmers along a riverbank. Three teens died, and a 20-year-old was injured.

Johnson, who has been held at the Marinette County jail since Friday, could be charged in the slayings as early as Monday.

Judy Johnson shared a home with her 38-year-old son and described him as a once-carefree father who became introverted after his wife left him seven years ago and took their two children to Ohio.

"He kept saying, 'I lost everything; I have nothing,"' his mother told The Associated Press on Sunday. "He just grew heartsick and started turning inward."

She said she didn't think her son had had a girlfriend since his divorce.

Police officers came to the Johnson residence on Thursday afternoon and left a business card. They didn't tell Judy Johnson that they were investigating a complaint that her son had sexually assaulted a woman on Wednesday at the river.

Her son returned to their home a few hours later, and she gave him the card.

"He seemed calm but looked like he was anxious to leave," she said tearfully.

She said he was probably "freaked out" over police interest in him.

According to police, Scott Johnson ended up at a bridge about 3 miles from the river hangout. Authorities allege he jumped out from bushes and opened fire on about a half-dozen young people relaxing by the bridge. Two teens ran to a nearby house, where the homeowner called police.

Killed were Tiffany Pohlson, 17; Anthony Spigarelli, 18; and Bryan Mort, 19. Twenty-year-old Daniel Louis Gordon was wounded. All were from Michigan.

When Johnson surrendered to police, he was dressed in camouflage and carrying a rifle.

Authorities have not commented on a possible motive for the shooting or said whether it and the alleged sexual assault might be linked.

Johnson has not been charged with sexual assault. Authorities have said they don't know whether he has an attorney yet.

Johnson was something of a regular at the swimming hangout, said teens who knew him. He even showed up a few days before the killings to help people off a rope swing over the Menominee River, they said.

"He was always really nice to us," said Conrad LaPointe, 14, who lives in the neighborhood. "But when girls were down there, he would just stare at them from the bridge."

Johnson occasionally built a bonfire near the river and would invite LaPointe and others to join him for warmth.

"Sometimes he'd say stuff like, 'I wish I could get a girlfriend,"' LaPointe said. "Otherwise we'd just talk about life, the world, whatever."

Judy Johnson said she is numb with grief, not just for her family, but also for the victims and their relatives.

As the case develops, "it won't just be him suffering; I'm hurting, too," she said.