Why this is a good concept
1: Ticking clock, obviously the lead has until the death sentence is carried out to find the killer and save his daughter. Preferably a short amount of time: Perhaps the final appeal fell through now the son has taken this action with only days to go.
2: An understandable bad guy: We can all relate to a son wanting to save his 'innocent' father from death row. (Just make sure to point out in the script that he went through all the correct and legal attempts to free his father before taking this drastic action)
3: An understandable good guy:? A father wanting to save his daughter is something the audience can relate to, not only that the lead can point out, he didn't convict anyone, a jury did.
In the script, (Not the logline) you might want to have a second bad guy, someone like the prosecuting attorney, who, as the story unfolds the audience discovers, rigged the system to get the 'win'