I’ve been reading through your assassin tag and I’m sure it’s circumstantial but what would be the time range for collecting the information they need to murder their target? Is it realistic for someone who’s been working 4-6 years to have accumulated a few hundred kills?
This is more of a world building question, because it hinges heavily on the organization your assassin is working for and the world they operate in.
In anything approaching the real world, probably not.
Okay, let’s run the math for a second. If you’ve killed three hundred people over four years, that’s going to roughly work out to a murder every four to five days. (If that’s spread over six years, it’s going to work out to be a murder every week.)
It’s probably feasible to have that volume of work, especially with contracts taking variable amounts of time to complete. However, that’s not the problem.
To put it mildly, murder is treated rather harshly by modern laws, meaning killing for hire is a fairly risky proposition. If you’re not being paid enough to take a vacation, you’re not being paid enough to kill people for a living.
Organized crime is a little different, and the overall volume can get that high. During the 1930s, it’s estimated that the New York Mafia carried out over a thousand assassinations. However, that wasn’t the work of a single individual. Which does raise a distinct possibility, an agency of assassins could potentially get into the range of a hundred hits a year, but it probably wouldn’t be an individual assassin.
Then there is Julio Santana, who has claimed to be the worlds most prolific hitman. He claims that he killed over five hundred people during his career, which spanned thirty-five years. (This works out to slightly over fourteen hits a year, which is extraordinarily high compared to other documented assassins.)
For a, “normal,” hitman, a kill per month is probably pushing it. The last thing an assassin needs is law enforcement realizing they’re active simply because the sheer volume got out of hand. More murders mean more evidence, and more risk of the police identifying a common pattern. On a long enough timescale, the probability of law enforcement putting everything together approaches 1.
I suspect there’s also a limiting factor with contract availability. Killing people is one of those professions where you really do need the customer to come to you. Just because your assassin could kill someone every week, that doesn’t mean they will have a contract every week. This brings their kills into further question when you consider that contracts wouldn’t be evenly distributed. I suppose it’s possible that a sufficiently infamous assassin could have a wait list, but fame is a very bad thing for an assassin. “Who killed this man?” “Maybe it was the world famous assassin sitting over there.”
(Actually, as a quick aside, fame is toxic for basically any profession that relies on being able to operate covertly. It doesn’t matter if you’re an assassin, a thief, a con artist, a spy, or even just an undercover cop, if you’re famous, that makes it effectively impossible to do your job.)
In fictional worlds, it is quite plausible, if the setting supports it. In some kind of fantasy or sci-fi dystopia, where an authoritarian state has sanctioned assassins, you could easily see a situation where an assassin has racked up a triple digit body count after a few years on the job. In that case they probably wouldn’t be doing their own research, instead taking what their organization handed them, and running with it. The staggering pace of kills would also be consistent with someone who’s simply taking assignments, and (relatively) poorly paid, because the work is legal and the risks are minimal.
A possibility that hews a little closer to reality would be a military sniper. Again, the body count is excessive, though there is historical precedence. Simo Häyhä was a Finnish sniper. During the Winter War (1939-40), he killed over 500 Soviet troops. This is even more impressive when you realize that the war only lasted 104 days. Häyhä is the record holder here, and racking up hundreds of kills in just a few years would still be fairly noteworthy. Very few snipers kill that many people, but it is possible.
One messier possibility would be an assassin who’s not particularly concerned with collateral damage, and uses explosives. A few well placed fertilizer bombs could easily get them into triple digits. Granted, this is more in line with a terrorist assassination, and not what you were thinking of, but it is one way you could see that many victims.
So, is it plausible for an assassin to be killing that frequently? Probably not, unless there are specific justifications. This doesn’t mean that it’s impossible, just extremely unlikely. Judging by what I’ve seen with ex-Mafia hitmen, forty to fifty is probably more in line a very busy assassin who’s been in the business for half a decade.