1-They might commit violent crimes.
Which would be a correct passive form expressing more or less the same idea:
2-Violent crimes might be committed by them.
3-Some violent crimes might be committed by them.
Sentence #2 is sentence #1 in the passive voice. Sentence #3 changes the meaning slightly, implying that there are some violent crimes they might not commit. (I would hope so.)
:)
I prefer the active- I see no need for the passive here, given that 'they' are unspecified.![]()