Okay, there’s actually an issue in here, so let’s step back and talk about professional criminals for a second. Criminal activity is their job, and they need to approach their life with a risk vs. reward analysis for nearly everything they do. They’ll work together and network with other professionals. This isn’t altruistic, just an understanding that they need to work with other people to achieve their goals. They don’t need to like the people they’re working with, but, if they all still have a shared goal, they will. Most understand how planning and advance setup can help reduce the risks involved in their profession.
Okay, with that out of the way, let’s talk about the crime. A kidnapping is not something you do spur of the moment. It’s a difficult criminal operation, involving a lot of moving pieces, any one of which can scuttle the whole operation after the team is committed.
Your criminal will need a team backing them up. They’ll need to have a way to grab and extract the victim, a place to hold them, a way to keep them alive and under guard while negotiating, a communications method that can’t be traced back to them, and a method to retrieve the ransom. Some of that can be dispensed, if they have no intention of returning the victim alive, or ransoming them at all.
Grabbing the victim is a little situational, but the difference between a successful extraction and a botched bloodbath is advance planning. Ideally your team needs to be able to grab the victim without leaving any witnesses behind. This is trickier than it sounds, because they can’t actually kill the person they’re intending to ransom the victim back to. Ideally this means picking a time when the victim and the victim’s relative/friend/whatever are at separate locations. If that’s not possible, the team will need a very delicate touch.
If the person paying the ransom dies, then the operation’s over, and the criminals have a corpse and nothing else to show for a lot of wasted effort. In some situations, they might be able to salvage the situation, by ransoming the victim to a new buyer, but that is an extreme long shot.
In a well run kidnapping, once the victim has been taken, they’re fairly unimportant to the criminals. They need to be kept alive, and they can’t be allowed to escape. But, they’re not the kidnappers’ focus. At this point, they’re going to be more interested in getting person paying the ransom to do what they’re told.
The other side of it is, with the extraction itself, your criminal will not want to leave witnesses. If they’re not the ones the kidnappers are planning ransom the victim back to, they’ll have no incentive to leave the witnesses breathing. Killing them sends a clear message that the victim is in serious peril, and it discourages the person paying the ransom from screwing around.
What this means is, your kidnapper isn’t going to grab someone “spur of the moment”. If he decides “now’s the time”, it’s because he was already planning to grab them. Also, there’s a very real risk he’ll simply kill your other characters. Best case the police don’t even realize there’s been a kidnapping, and worst case, they’re no closer to identifying the kidnappers. As opposed to the police now having at least a physical description of one member of the crew. So, I guess the real answer to your question is: two shots to the chest, one to the head.
As a quick aside, if his plan is to force one of the characters to do his bidding, he might just grab them all, and release the one he intends to use as a pawn later, and keep the others as hostages.
Once they’ve got their victim, there’s the question of what they want. If the goal is money, then we’re talking about a ransom, and there’s a lot of literature on the subject. If they’re wanting to force someone else to do what they want, they’ll need the ability to micromanage that person’s actions. Usually we’re talking some kind of communications setup with the pawn, but surveillance isn’t out of the question. If the objective is information, then everything gets a little messed up. I’ll stick a pin in that for later, partially because a discussion on interrogation and torture will rate a trigger warning.
Spartan, the first season of 24, Man on Fire (2004), and Taken should all give you some insight into the kinds of people you’re dealing with. 24 opens with using captives to force the protagonist to do their bidding, and the first 12 hours are really good. Man on Fire (2004), is a kidnapping for money. Taken and Spartan both deal with selling captives into sex slavery, which is something I just glazed right over. Both films illustrate how this particular form of kidnapping operates in a more opportunistic assembly line nature, because of how they’re generating income.
For some additional insight on professional criminals, I’ll keep recommending Heat until you watch it. Ronin and Reservoir Dogs are also worth watching. Technically Ronin is dealing with former spies who’ve become mercenaries, but the same principles apply. Ronin also has the benefit of actually being a smash and grab operation, even though the target is an attaché case, and not a person.