Property LPed.HasBeenBooked
I'd like some sort of hook into whether an LPed has been delivered to a police department (the cutscene is playing to remove them from the vehicle) or has been taken in by another unit for prisoner transport (they are now in the back of the transporter), so that I can hook in with a third-party mod to provide a small financial reward for the arrest (e.g., $50). Currently, in spite of Niko Bellic's impressive resumé on McReary's desk computer, he is not paid for his services except when he writes bogus traffic tickets, which is pretty much the exact opposite of how payment happens in real life! =) (Not that police are paid a commission or quota in real life or anything, but at least getting some bonuses for the work you do ties the mod back into the game instead of being merely for fun. Paying a wage based on time spent on duty is easy, but bonuses are a time-honoured convention of the GTA series.)
The only mod that currently exists out there to give payouts just runs in parallel (without the API) and gives a cash reward when you target someone and press the E key, so it's a bit of an unsuitable solution (it can be exploited by targetting anyone and hammering the E key, even when not on duty -- and is also severely incompatible if another mod wants to use the target+E for anything else -- and its solution to the problem is basically "scout's honour", which is a terrible form of game design... unless you're playing Calvinball ;-)).
Method LPed.WasPlayerInvolvedInArrest(Ped player)
I'd also like a boolean that flags positively only if the player was actually instrumental in the LPed's arrest in some fashion -- this one is a bit harder to define semantically, but most simply, it would require the player to have gotten out of the vehicle at least once during the chase and to have targetted the NPC at least once. Otherwise, this would mean that the player more or less allowed the NPCs to handle it, contributing only in a de minimus sense at best.
To be properly generic and to work for multiplayer it might be necessary to track this data for any arbitrary number of officer peds, which gives potential for non-existing object script errors, so ideally it would be limited to tracking only peds that are found under any connected client's Player class.
This one is a huge can of worms, though, so it might be much harder to implement -- it would require, at a minimum, a tick-based script that flags when an LPed has been targetted and when the player has gotten out of his police vehicle, and which sets another flag if both conditionals are true. Resetting the flag is at least easy, since it can just hook onto the Alt+E 10-8. Based on difficulty it might better be left for a third-party mod, but I'll put it out there anyway since a good API exposes just about every logical event. =)