At the Belter crime scene, it is mentioned that the ballistics expert had determined the gun had been fired twice. At that point it would have been impossible for him to determine that at the crime scene alone. The gun in question was referred to by Spudsy, Mason, and on the pawn sale as a .32 Colt automatic.
When Perry is in Locke's apartment, he starts dialing the number on the wall phone before picking up the receiver.
Perry Mason repeatedly refers to the murder weapon as a .32 Colt "automatic". The gun is a semi-automatic.
Bill Elliott's character name is spelled "Carl Griffin" in the credits, but a newspaper report spells it "Carl Griffen".