Informants are easily spooked and they’ll prioritize escaping at the first sign of trouble. They don’t travel along as well; it’s either they’ll part of a small group or with a bodyguard. In any case, the best way to capture and interrogate an informant is by eliminating his crew/bodyguard silently then quickly nabbing him before he gets the chance to escape.
If ever you spooked an informant prematurely, you can ignore his crew altogether and chase after him. He’ll enter his car and make a run for it. If ever you’re quick enough to reach his car and open the door before he can start the engine, you’ll be able to kidnap the informant and drive his car instead. This will become a “Drive like a Madman” sequence where you have to do all kinds of dangerous driving stunts like driving into incoming traffic or near misses to terrify the informant until he croaks up and gives you the information you need. If ever the informant escapes your grasp, don’t worry; he will relocate to another spot where you can attempt to capture and interrogate him again.
For this objective you have to hunt down and interrogate one of the two of Charlie Kincaid’s informants. (Seems to be randomly selected by the game) The first one is found in the diner with one bodyguard. This one is quite easy to get rid of so kill his bodyguard stealthily (recommended) then quickly subdue him.
The other informant has a couple of guys with him, beating an unfortunate soul. There are other people so use your intel view to identify the enemies. The quickest way to deal with them is by letting the lookout see you long enough then hide quickly to trigger a search. Once you isolate him, you can now stealth kill him. Next, hide near the truck and throw a Screaming Zemi away across you so that they’ll turn their backs on you and investigate it. Take out the other crew member then finally, you can easily subdue and interrogate the informant.
You have the option to either kill the informant or spare him and recruit him instead. The latter is the best choice since spared informants increase your racket’s earn, allowing you to have more kickbacks. The next objective of the mission will now be unlocked.