Well, that’s their job, among others. They don’t investigate, don’t interrogate, they just arrest. Then turn the person over to the appropriate authority.
Speaking as a sister-in-law of a US Marshal, they are there to get the job done, and that’s it. If the Marshal Service is called in, it’s their job to get in there, find someone, and turn him over. I’m suprised Shank agreed to a television interview. I mean, it may be interesting to hear about how they caught the guy, but it’s not like they can give any information out, anyways.