Might depend on the locale as well, i.e. in a large jurisdiction, the supervisor might be less likely to get out in the field than in a small one. You might just contact the Marshals Service and tell them you're an author in search of a little accurate information and describe the scenario(s) you have in mind. They might be nice enough to respond.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken