Quote Originally Posted by Ludens
EYG, I think you are under the misconception that assassins can actually catch other assassins. This is not the case, or at least, not as far as I know. Only BF and spies can do that. Spies do get the credit, even though it was probably the border fort that did most of the work.

Hi Ludens,

1. The dialogue says that the captured enemy agent was an assassin.
2. Sometimes it also says they "confessed that the XXXX filled their purse"
3. These catches were in provinces where I deliberately had NOT built a BF
4. My 0 or 1-star assassin there gained a star as a result of the capture
5. This began happening long before I'd been able to build the facilities for spies.

You're right that you can't purposely target enemy assassins, because you cannot see them on the strategic map but this 'policing' function is an ability assassins have had ever since STW (spies/shinobi too, of course). Maybe I know the game too well?