MM series -

I just remember reading the very beginning some time ago --

-It involves Law Enforcement (cops, FBI, US Marshals, etc)
-A man is in protective custody, possibly before testifying in a trial (though maybe not)
-Someone gets a blow job, which is against protocol and a big no-no. I think they're even caught.

That's about all I remember.
I think it was part of a series and was the first book of the series.

Pretty sure Manjuu solved this for me: Hank Edwards' Holed Up (Up to Trouble #1)