****SPOILERS*** Let. Det. Mike Stone, Karl Malden, and his partner Inspector Steve Keller, Douglas Keller,have their hands full in proving that ex-convict Artis Pierce, Kez Grars, is responsible for the death of young Johnny Hobbs in a home invasion that he pulled off by his father Robert Hobbs, Ed Nelson, an eye whiteness not cooperating with them. In that Hobbs refuses to identify Pierce as his son's killer. That with no real evidence in proving that Pierce killed Johnny it's decided to try him for breaking and entering that can only put-him as much or little as a year behind bars and Hobbs wants nothing of it. In fact Hobbs plan is to allow Pierce to go free and then like Charles Bronson in the movie "Death Wish" take him out, not to dinner, by himself vigilante style.
The one thing that could convict Pierce in Johnny's murder is an hearing aid that the hard of hearing Pierce, who claimed that he didn't hear his rights read by Inspector Keller, left at the scene that can prove that he was there that was overlooked by the police. And it's Let. Det. Stone and Inspector Keller's job to find it before Hobbs finds Pierce and ends up murdering him that can put him behind bars as well. The good news is that Hobbs is so incompetent in doing his job as a hit-man that in the end he helps not hinders the police in arresting Pierce for his son's murder.
***SPOILERS**** It's by trying to gun down Pierce Hobbs leads the police right to him in his shabby hotel room where Hobb's is planning to off him as soon as he comes staggering home from drinking and pool playing all day at his favorite ginmill. But the real deal in getting Pierce busted is that his missing hearing aid is found at Hobbs' house by Inspector Keller but now it's up to the SFPD to not only arrest him but keep Hobbs from murdering Pierce before he gets to him. It was in the end that Hobbs butter-fingered attempt to murder Pierce that saved his for a stay behind bars for some 10 to 15 years. That by Hobb's messing up his sloppy attempted assassination of Pierce, like he did twice before,thus giving the police enough time to arrest him and, to make sure that it sticks, have his hearing aid on for them to read him his rights to hear every single word.