story – How might investigating a prison break be accomplished?

I can’t think of a way to concisely fit my entire question in the title, but here goes.

I’m currently running Dark Heresy 2e for my group, as my second time GMing a game (the first time was short-lived, and hardly counts). They’ve successfully tracked down and captured a recidivist who recently escaped from a prison world, but I intend for them to investigate that prison world next and find that not only was she broken out by an outside force, but that the party in question was hired by a rival Inquisitor with a grudge against the group’s employing Inquisitor.

The planet in question is not yet fleshed out, so the answers to the following questions might help me accomplish that.

With background out of the way, here are the questions:

  1. How might someone break a small group of prisoners out of a penal colony and get them off-world? I want to make it believable that the person who broke them out was a professional, but also make it not too hard to figure out for a group with a couple rookie RPG players at low level. My brain is kind-of bricking right now; I can’t think of something interesting that isn’t too easy or has already been done.

  2. How can I drop hints that it is this rival Inquisitor without making it plainly obvious, so that the party can’t simply take the evidence to a tribunal and have him arrested? Ideally, they find tangential evidence, enough that their Inquisitor is sure that it’s him, but not enough to have a trial, so that it’s up to the party to chase him down.

Any additional advice you could offer is also appreciated.