Cage of Evil (movie, 1960)

While investigating a diamond heist, disgruntled cop Harper (Ron Foster) falls for Holly (Patricia Blair), the top suspect's main squeeze. When she convinces him to kill her boyfriend and make off with her and the loot, they start down a treacherous path full of dark surprises. Directed by Edward L. Cahn, this crime drama co-stars Harp McGuire as Murray Kearns, Harper's persistent partner who stumbles upon the pair's devious plot.