The crime is almost unimaginable: A precious 5-year-old boy named Kenny was shot by his own mother, a single bullet to the head while he was sleeping. Then she turns the gun on herself.

The tragic murder-suicide in Montana on the night of March 5 shocked the community and left Kenny's father stunned.

"Got there two hours after he died," said Ken Kreuscher Sr. "He fought for his life for over 12 hours."

Crime Watch Daily Denver affiliate KDVR reports that just days before killing her son, Sara Atkinson took little Kenny on the road, driving nearly 500 miles to Montana to visit family. Ken Kreuscher, the boy's father, was terrified. He says he warned Denver Child Protection Services that his ex-wife might harm their son. He says they ignored his pleas.

"I've been telling everyone in court this was a possibility that this would happen," Kreuscher told KDVR.

Kreuscher divorced Atkinson a few years ago and fought to gain full custody of Kenny. Kreuscher told child protective services that she was mentally unstable and paranoid. He says she believed there were bombs planted in her home and cameras in Kenny's shoes.

"Just erratic mental illness everywhere. No one really helped me," said Kreuscher.

Kreuscher says his ex-wife was dangerous, even violently attacking their 5-year-old boy.

"I saw a huge mark recently on Kenny," said Kreuscher. "He told me his mom punched him. I filed a report."

Kreuscher documented the abuse his son suffered at the hands of his mother in a heartbreaking video recorded just days before Kenny died.

Kreuscher says he showed the video to a CPS caseworker, who said there was nothing she could do.

"And she stood in front of me and pointed at my closet and said 'Unless your kid is being stuck in a closet every day or beaten every day, I'm not going to do anything about it. And if you call back, if I hear back from you about this kind of stuff, I'm going to take him from you and her,'" said Kreuscher.

And if that's not bad enough, Sara Atkinson hired a private investigator, who does not want to reveal her name, to follow Ken Kreuscher during the custody battle. She was trying to show that it was her ex-husband who was abusing the boy.

"My instinct said she might take Kenny and run, maybe leave the state, but I never thought that she would physically harm the little boy," said Kreuscher.

Looking back, the private investigator says there were red flags, and recalls Atkinson issuing a chilling warning.

"She was afraid that the father was going to take the child from her and she said that she would kill him before she would ever let that happen. That she would shoot him and herself," the P.I. said.

That threat became a horrifying reality. With the shocking news of Kenny's murder, the private investigator says the child protective services agency has blood on its hands.

"We have cases where we've gone to Social Services and said 'These children are being abused, we have documentation on it,' and they turn us away," the P.I. said.

The frustrated P.I. says just like Ken Kreuscher, she reported the dire situation to Child Protection Services, and says they did nothing to help the young boy.

"I really would like to see something done, because how many more kids have to lose their life and be caught in a crossfire because social services doesn't help or somebody doesn't believe one parent?" the P.I. asked.

Denver Human Services issued a statement following the boy's death: "The loss of this child is an absolute tragedy for this family, their loved ones and friends, and for our community and agency. We are working to understand the circumstances surrounding this horrible act."

But this statement does little to ease the excruciating pain of a father who lost his beloved son in a tragedy he says could have, and should have, been prevented.

"I'm here because I don't want this to happen to anybody else," said Ken Kreuscher. "It's not right what they did."