When Perry visits Hugo Burnette's apartment, one of the buildings seen through the window has a tall flagpole on its roof. The American flag on that pole is almost fully extended, as though the wind is furling it. But the flag is motionless, thus revealing that the background neighborhood is probably a photograph.
One of the buildings outside Hugo's office (which is said to be in New York) has "The Times" near the top (the whole window image is a painting or photograph.) "The Times" building as portrayed is actually the Los Angeles Times building in downtown Los Angeles.
The defendant spends considerable time standing beside the open door of a coupe without noticing a dead body lying in the back seat.
When Lt Tragg and Hugo Burnette are viewing the body of Margaret Ralston (thought to be Lucy Stevens), Tragg mentions that they found the driver's license of Lucy Stevens on the body along with other items of ID. The police should have compared the thumbprint on the license to the corpse before bringing in witnesses to ID the body...
At 10 minutes in, the actor on the left when raising his eyebrows, his hairline moves drastically.