You will want to have a more specific theme for your poem, I think. Crime prevention is a pretty broad category. What came to mind when I read your question was the idea that much crime prevention lies in community policing, the idea that the police have to really be part of the community, on the ground, so to speak, knowing everyone in the community very well. Most people are not comfortable writing poems that don't rhyme, so you might find it easier to write a rhyming poem. You could do this in rhymed couplets, where you have two lines in a row that rhyme and alternating, for example, the second and fourth in a verse of four rhyming lines is another possibility. Here is a brief example for you on community policing:
Cops can't just ride around in cars.
They need to walk the streets, wide and far.
They need to know the kids and the grownups, too.
They need to keep everything close in view.
There are other themes you could pursue, for example the "broken windows" theory of law enforcement, which is that if you take care of the little things in the neighborhood, graffiti, broken windows, and trash, for example, the big things tend to take care of themselves better. Another theme in crime prevention is more social in nature, that taking care of hunger, jobs, housing, and education will result in a reduction in crime.
This is an interesting assignment, one I am sure you will do well with once you narrow things down a bit. Keep a thesaurus at your side while you write your poem. It can be such a help when you're stuck for a word.