An incisive detective imprisons a man who is murdered in prison while innocent, so he resigns out of remorse to free unjustly incarcerated people in defiance of the system he once defended.

Unless this is for a TV show, I would try personalizing the logline. For instance, instead of working to free unjustly incarcerated people, the story should be about a specific incarcerated person, and the stakes should be high.

"A detective races against the clock to prove a prisoner sentenced to death row is innocent, motivated by his own guilt of once putting a man behind bars who was posthumously found innocent."

Is great that you provide a source of internal motivation or drive for your protagonist; however, it lacks an external conflict or some sort of opposition or obstacle.

A rewrite might look like

After imprisoning an innocent man, a remorseful detective works to free the unjustly imprisoned, until (insert external conflict).

I would trim it a bit, perhaps something like this:
An incisive detective imprisons an innocent man who is murdered in prison, resigns in order to free unjustly incarcerated people defying the system he once defended.
When an incisive detective resigns for imprisoning an innocent man who is murdered in prison, he defies the system he once defended by freeing unjustly incarcerated people.
When a remorseful detective resigns for imprisoning an innocent man who is murdered in prison, he defies the system he once defended by freeing unjustly incarcerated prisoners.
I hope this helps.