Is there a Latin equivalent to the English phrase "on the run" to indicate someone who's avoiding capture/recapture? For example, "The prisoner is on the run." Would something like in fuga be accurate, or would I need to settle for something like Captivus effugit?
The closest phrase I could come up with is in fuga, which is quite literally "on the run". There are a number of classical attestations of this phrase. Another good choice is the participle fugiens, possibly with a prefix ef- or pro-.
There is no Latin phrase that behaves exactly like "on the run", so you have to judge each context separately. For "the prisoner is on the run" I would simply say captivus profugit. For "while on the run, the prisoner slaughtered a dog", I would choose either captivus profugiens canem necavit, captivus in fuga canem necavit, or use two personal verbs like captivus profugiebat et canem necavit. The choice is a matter of style and fluency.