Toward the end, Buck Gerard is hiding in a locked closet. Matt Nolan (James Cagney) tries to open the door, and it is visibly moving. An interior view of the closet shows the door is not moving at all.
The stock footage of New York streets/traffic is exceptionally grainy contrasting the otherwise high quality photography of the staged scenes.
Although the story takes place in New York City, it's apparent the exterior scene with the three taxicabs was filmed in Los Angeles.