A lot of criminals are remarkably stupid. It's fun to imagine criminal masterminds making up a lot of their plans with meticulous planning only to be foiled by the heroes. But in real life most crooks are fairly dumb. Even intelligent people who do crimes can make mistakes that come off as remarkably stupid to people learning about them.

I watched a lot of episode of Forensics Files and other shows that document cases that were solved by slim margins. Some criminals on the show really did almost get away with it if it wasn`t for one tiny mistake. In other cases, however, they got caught ultimately because they left behind something that absolutely would have lead to their capture.

Like in one case there was a mugger who killed a college girl while she walking home. The area she walked through was wooded and dark. The episode documents how DNA was used after it had advanced sufficiently to get him and they had to track him down to get a good sample. But there is something absolutely critical that the show didn't point out: He got on police radar because he dropped a bag of his that had a medicine bottle with his name on it. If he just picked up his bag the police would have had nothing to go by at all.

The other problem is that planning a murder like the one for Brian Thompson and getting away with it is hard as balls. Other than the fact that there are cameras everywhere. The guy needed to be at the right place and the right time and be there for only a minimal amount of time (to not draw undue attention) and he also had to be sure that there weren't that many police around so police response times would be extended. I think he did it at the time because he also knew that the police change shifts so there are fewer beat cops around.

Also the silencer obviously doesn't make the gun 100% quiet, but it was done to make it quiet enough to not set off the shotspotter towers. Those towers are more and more common in many cities so that when a criminal fires a gun, they can quickly triangulate where the shot was fired from. This would give away his location very quickly and minimize police response time.

It is meticulously planned. But there could be any number of things that could have gone wrong. The gun could have simply not fired at all. There could have been a few cops working extra hours nearby and ran after him quickly. Someone could have jumped at him to stop him right away. Lots and lots of factors go into it.

Even some people said that why was he using a hostel (which has security cameras and other witnesses) when he could have rented an AirBnB apartment. Some places rent rooms and apartments for people and those people never actually meet the host, meaning there is no one who would see you.

As for how to pay for them... the guy could have used a prepaid cash card, one bought and charged with cash. It cannot be traced back to you easily, if at all.