PC Andrew Harper's widow Lissie Harper said that it was "heartbreaking" he didn't get justice.
A year after the death of the brave police officer, his wife has spoken out about her "overwhelming sense of disappointment" on Good Morning Britain.
Lissie Harper was a young newlywed when PC Harper was killed as he tried to apprehend quad bike thieves on August 15 2019.
She is campaigning for Harper's Law, which would mean those who kill emergency workers are jailed for life.
She told Piers Morgan and Susanna Reid: "We need some form of justice should the worst thing happen to them (emergency service workers).
"Losing someone in that way you can never prepare yourself for.
"Just dealing with the grief is a tremendous effort, so when it comes to the court case you do just think well you know this is going to be hard but we'll get through it and at the end of it Andrew will have some justice.
"For that not to happen is heartbreaking."
Lissie continued: "I felt an overwhelming sense of disappointment for him because I thought that he'd been totally let down and that's what brings me to creating this new law that it's something to make a change that we all can see really needs to happen."
She added: "I want to create a brand new law that sees our emergency service workers protected for the job they do."
All three of PC Harper's killers were spared life sentences, and Lissie launched the campaign for a change in the law to see that all criminals stay behind bars if they are convicted of killing a police officer.
The petition has more than 650,000 signatures.
Good Morning Britain airs weekdays at 6am on ITV.