I'd also come to this conclusion from watching movies like Lock, Stock and Two Smoking Barrels and TV shows like Sons of Anarchy.
If you're going to run a crime/cyberpunk style scenarioyou might like to try mapping these relationships out as a node network to help you visualise where your plot might end up. Fans of the indie RPG FIASCO will be familiar with this concept as the basis for character generation albeit on a much simpler level. Taking my favourite crime TV show "Sons of Anarchy" as my inspiration I made this relationship map to illustrate my point.
|Sons of Anarchy Relationships Map|
(Click to embiggen)
Whilst far from accurate, it demonstrates that often overlooked minor characters can have unexpected or glossed over connections with otherwise unconnected groups.
For example in the Sons of Anarchy universe:
Chuckie Marstein is an often overlooked minor character often seen hanging around TM, working behind the scenes at TM, in the bar at the clubhouse, serving at the ice-cream parlor or running errands for Gemma. However, his backstory also reveals he was Otto's cellmate and friend in Stockton County Jail, and that he was the Bookkeeper for the Lin Triad who'd stolen two of their counterfeit money printing plates. He's also done his fair share of work for SAMCRO such as wanting to be an amputee porn star so the gang could gain access to Georgie Caruso's porn studio when he was working for Otto's wife Duanne Laney as the Cara Cara bookkeeper. There's also the unrequited love angle, as he holds a torch for Gemma after she bought him new prostethic hands.
Brooke Putner is another minor character who joined the show as a crazy teenager who blamed SAMCRO for her mother's death. In fact it was Jax's father John Teller who collided with their car killing both himself and Brooke's mother Emily, although the show hints heavily that her mother is in fact alive and living on the streets as we see her picking through dumpsters every now and then. Brooke has since fallen in love with Ratboy, helped out at the clubhouse and now works for Gemma as Abel and Thomas' nanny. This close proximity to the centre of the SAMCRO empire means that it's only a matter of time before she gets hit by some of the club crossfire.
Visualising your crime network in this way makes it easier for you to write convincing plots. You can see what the effect of an NPC death might be. If Gemma were to be killed would Chuckie take out his own type of vengence on her killer or if Ratboy were killed in some accident would Brooke hire Happy to hunt them down? The consequences for larger characters tend to be more obvious, say if August Marks is taken out of the game someone will fill the vacuum, but who?
One of the things I love about the show is that when SAMCRO try to get themselves out of a bad situation, their actions always have unforseen consequences which almost end up burying them. Your game should be no different the PCs should always be making a hobson's choice with the information they have at their disposal, it's not their fault that the guy they killed in revenge is actually a key player in an even bigger, more powerful crime syndicate. It doesn't rain.... it pours!