I don't know what you responded to, it's deleted now, so I can only address your question directly:

Reputation. If you know a reliable killer across the Atlantic but don't know one in America, it makes sense to smuggle your known reliable killer in rather than risk talking to a police officer posing as a contract killer. Even in "extremely violent America", if you start asking around for contract killers most people will get weirded out and tell the cops to take a look at you.

(The comment had suggested that his killer was likely brought from Nigeria.)

The "ban on international travel" is a rather pertinent part of that question, oddly enough. The kind of people that are capable of magicking someone across two closed borders and an entire ocean tend to not lack contacts in either country.

Having criminal contacts in both countries doesn't necessarily mean somebody trusts their criminal compatriots in both countries. Particularly when you're talking about a crime that's more severe (murder) than what they're normally trusting somebody with (smuggling perhaps.) I'd guess there are a lot of informants in organized crime. It seems the sort of business where the least trusting survive the longest.

If somebody took the risk to find a contract killer once and didn't get caught, it makes sense to me that they'd try to avoid taking the risk a second time by using the same killer.

Keep American jobs for Americans! ;)

However, perhaps they just couldn't get the right killer at the right price? Or maybe they're scarcer than you think? We keep hearing immigrants are taking American jobs, but in reality they're taking the jobs no American would take in the first place, so this may be more simple supply/demand...