When a hero dies, it’s hard to understand especially when it could have been prevented.

“He was the most selfless man,” said Trooper Damon Allen’s widow, Kasey.

Allen and his wife were teenage sweethearts. She laughs at the memory of how they met. She was 17. He was 16. They met on the job at McDonald's.

“He was the cook, and his mother was the manager,” his widow said, chuckling.

They married young -- so young that she was his legal guardian and signed his high school report cards. They didn’t have much money for college. He got a job with the Texas prison system because if he worked there five years, he could apply to be a state trooper.

“Damon wanted to be a cop from the time I knew him,” said Kasey Allen, a paramedic.

On Thanksgiving, the father of four spent the day with his family and then went to work. As a trooper, working the holidays was just part of the job.

“The last thing he said to me was that he loved me and he’d see me tonight,” she said.

That night, Allen encountered Dabrett Black – a man with a history of attacking cops -- during a traffic stop on a stretch of highway in Limestone County, south of Dallas. Their initial interaction was cordial. But then authorities said Black pulled rifle from his car and shot Allen in the head with a rifle.

“We've known that there were those that target law enforcement,” she said. “The only shock was that it was my husband.”

Allen died just days before their 24th wedding anniversary.

There is no doubt that Black is a man who slipped through the cracks of the criminal justice system.

In 2015, Black severely beat a Smith County deputy on the side of the road. The deputy suffered a broken nose, two black eyes and needed six stitches to close wounds above both his eyes. In a car, video captured him bragging about how he could have killed the deputy.

“Somebody supposed to be scared because you got a badge and a gun,” Black said, according to the recording. “I showed you what your badge and gun ain't s***. I whipped his a** without a badge or a gun.”

Black looked straight into the camera and said, “Just imagine if I had some weapons. Do you understand that?”

Kasey Allen said Black fulfilled his promise.

“I think it showed that he was extremely violent,” she said. “It shows that he obviously was targeting law enforcement.”

She is angry that Smith County prosecutor Jacob Putman cut a plea deal that dropped a felony down to a misdemeanor. Black was sentenced to one year in jail when he could have gotten up to 10.

“If that’s what he would have gotten, he wouldn’t have been allowed to be out to pull the trigger,” she said.

Putman agreed to the deal without the permission of his bosses in violation of office policy. An audit has since discovered that Putman reduced or dismissed almost 80 cases in violation of office policy since 2013. Several of those occurred after he was reprimanded for violating the policy in 2016.

Kasey Allen believes Putnam’s decision cost her husband his life.

“You prosecute him to the fullest extent of the law,” she said.

Putman – now running as a Republican candidate for district attorney – said he cut the deal because the deputy was not willing to testify. He also has previously told WFAA that he misunderstood the policy.

Last month, she encountered Putman at a DA debate. She said he told her he was sorry. She does not believe it was sincere.

It has since been revealed that Putman made a complaint with the Texas Rangers on one of his bosses about a week after a WFAA story aired the dash-cam recordings from the earlier Black case. According to the Ranger investigation, he told the Ranger that “he did not really care if the information was acted upon and was reporting the criminal violation in order to assure he was afforded ‘whistleblower’ protection should Mr. Bingham try to fire him.”

The Rangers have since concluded there wasn’t enough evidence to warrant a criminal investigation.

She is now backing Putman’s Republican opponent.

“He tries to blame everyone else for his actions,” she said.

At the time of her husband’s death, Black was out on a low bond after another case involving an attack on police. Black fled from police last summer and rammed into the SUV of a deputy. That’s why she met with the governor last month to push for changes to bail bond laws.

“I don’t want anybody to fall through the cracks and the loopholes in the system. I want everything to be standardized and fair,” she said. “If you're going to have something horrible and terrible happen to you, you can either wallow in it, or you can take it and use it to affect change,” she said.

She is also reaching to other widows through Cops 4 Cops, a group that works with the families of fallen officers.

“It’s something that I can go in and I can literally say I know what you’re feeling,” she said. “I know what your kids are feeling. What you’re having to through as a mom. I remember having to tell my children your dad’s dead. I’ve done all these things.”