They have lots of data -social media foot print, addresses, names of friends, coworkers, etc. who they call, where they go for coffee; or happy hour after work, quite literally everything they can get on these guys.
They the. Give it a known list and tell the machine to look for patterns (like switching burner cell phones every so often.) consistent between all of them.
It even weights lower strength correlations as softer evidence.
They then take that and run it against everyone they have in their database. And it spits out people that match the same things.
As for it being artificial intelligence- it is, just not general AI (Like Data in Star Trek, R2-D2 in Star Wars or Kryzen in Red Dwarf). They’re more like idiot savants that are very good at this one task and suck and literally anything else.
The problem is mostly in the shit data it was programmed with; and an assumption that it would always be right. It can recognize patterns, but there’s always some natural variation in the pattern.