"can of worms" = an unforseen troublesome situation, a sudden complexity
"bookie-cricketer nexus" = There is some suspicion that Woolmer was involved in illegal gambling, and as a result, some believe that he was murdered due to his knowlege of match fixing; that is, one of the players on the team was giving information to a bookmaker, or a "bookie", and then deliberately throwing the game after a number of large bets had been made. Authorities are now trying to find out if there is any truth to this theory.
I think the UE definition leaves out an important part of the meaning. The defining feature of a 'can of worms' is that it's sealed. Yes, it's got nasty and possibly complex things inside, but the public needn't be bothered by them (as long as nobody opens it).
At the time of writing, it has just been disclosed that this was murder. I can only say that this is a totally awful situation. There can be never be any acceptable reason for anyone to kill someone.
A can of worms describes a very complicated state where it is extremely hard (and probably impossible) to identify any particular subject with any confidence, but also and at the same time, it may describe a state where the subjects of the investigation are deliberately trying to hide their true positions, while ALSO being something not nice to look at and something you don't really want to dig into. (who feels happy poking around in a can of worms?)
Most people find a handful of worms intensely revolting! Most worms look the same and they wriggle around so much together that even it you targetted one specific worm, a fraction of a second later you wouldn't be able to tell which one it was that you were looking at, or where it was in the can.
In other words, to open a can of worms is to look into something horrible which will inevitably have a great number of outcomes, non of which you can identify and which could easily result in a lot of unexpected nastiness, whereas if you left it shut you'd not be bothered by it.
No, the bookie takes the bets. The players, if they were fixing matches, would take money off the bookies to lose games, etc. The nexus (connection) is between the bookies and the players to fix games or get information that they shouldn't.
NB As this is a controversial matter going on now, I am not implying that there was corruption going on as I have no idea at all.