I’m going to sketch your scenario. First the basic scenario were crooks fire a gun alone. In black is the report and in blue is the Mach cone that produces the crack after 0.1sec.
Now your scenario is a gun fired from the back (in the small red circle) ahead in around 0.09sec before Crooks “fake” shot. For this scenario the gun used by crooks would have to be fired with a delay by some remote device. Then the gun from the back has a suppressed report represented in dashed black circle.
Now can you see the difference from the 2 scenarios? The Mach cone from a fire from behind (represented in yellow) is not suppressed like the report. Therefore, it will reach Ross audio before the “fake” report, keeping in mind that the crack from the first real scenario would not reach this audio. Since there is no audio of crack of the first bullet on Ross audio therefore this suppressed gun theory is not possible.