Corrected entry: No reason is ever given as to why Detective Bowman would murder a woman for her jewelry.
Correction: A plot hole is when there is a logical inconsistency that benefits a story despite not making any sense. A reason not being given for a character's actions is not a plot hole, nor is it any other kind of mistake.
Not only is it not known why Bowman killed the woman, no explanation is ever given as to why he chose to frame Walker so it still benefits as a plot hole.
Correction: It should also be pointed out that Bowman didn't murder the lady for her jewelry. While his motives were unknown (and irrelevant), he simply used the jewelry to frame Walker.
Bishop73