Four mafia members rob a bank...

Tom was a member of the mafia, along with Dick, Harry, and John. One day, they decided to rob a bank. They ended up deciding that Tom was the main robber, Dick the getaway driver, Harry backup muscle, and John the lookout.

The day came and Dick drove them all to the bank. Tom got out first, followed by Harry then John. John entered a nearby building to watch the streets from the roof, where he had previously set up a sniper rifle, Harry went into the bank, with a gun in his pocket, and Tom went up to the till, also with a gun. Dick, of course, being the getaway driver, remained in the car.

Tom went up to the till and requested to withdraw £250 from his own account. Not having been threatened at all, the teller obligingly did so, but had to turn away to get a few spare £50 notes.

While the teller was doing this, Tom planted a small, powerful explosive near the corner of the glass barrier. Tom then walked away after putting the £250 in his wallet, pretending to exit the bank, when he detonated the explosive.

In the confusion caused by said explosive (the staff having secretly pressed the alarm button to silently alert the police), Harry and Tom broke down the "Employees Only" door and threatened the staff to show them to the vaults. The staff obviously complied, and opened the vaults for them, allowing them to abscond with £200,000 in total.

The police arrived and John was doing an excellent job keeping them at bay with the sniper rifle. Tom and Harry both ran out the bank, with Tom first entering the car while Harry joined the crossfire. John, seeing this, saw that it was time for him to get into the car, so he ran down the steps, and entered the car too. Harry then made it in and they sped off back to their base near the Thames, somehow losing the police in the process.

Having made it off the radar, they now had the problem of dividing the pickings. Tom, of course, argued that since he had planted the bomb, he should deserve the most share, since the operation could not have gone well without that critical step. John argued that had he not been there, the police would have arrested the other three, and that they should show some respect. Dick argued that he had done everyone the favour of shaking off the cops, and Harry merely said that everyone should all get equal amounts for doing the same amount of work.

Tom then said that Harry didn't really do anything. Harry argued that John had abandoned his post. John said that any competent driver would have stopped the cops from following them, and Dick said that anyone could have done Tom's work.
The argument in this manner escalated, and eventually it turned into a physical brawl. Over the course of the brawl, Tom grabbed the £200,000, but was then pushed by Harry into the Thames! Tom unfortunately never learned how to swim, and so promptly drowned.

When the other three noticed that their earnings had been waterlogged, they all jumped into the water to retrieve it. Thankfully, they were able to recover the full £200,000, as well as the £250 in Tom's wallet.

However, the notes were all slimy and dirty from the sewage in the Thames, and so rendered nigh-unusable.

A silence was heard between the three. It was soon broken by Harry, though.

"Before we split this money up... let's make sure we launder it."

[x-post /r/punny, didn't want to ruin the joke by placing this in the title.]