In February 2017, Katia Kelly was walking through her Brooklyn neighborhood when she saw a $3 million brownstone in a state of disrepair. After finding out that the property was owned by Manafort (who isn't merely rich, but "spent over a million dollars on business suits" rich), she spilled the beans on her blog and started to dig into the property's financial history. Eventually she stumbled upon a series of shady-looking transactions that looked an awful lot like he was trying to disguise the source of his money. Seems his fancy suits weren't the only thing he was laundering.
As you can't keep a good neighborhood watch down, Kelly asked around for help decoding the byzantine money trail and roped in two other neighbors, Matt Termine and Julian Russo. What they found was a string of loans, sales, mortgages, permits, and other activity concerning not only this particular dump, but several other Manafort-owned properties.
The New York TimesFrom there it gets a little complicated, but here’s the TL;DR version.
Figuring that this needed its own home on the web, they started a new blog to host their findings, which were immediately picked up by The New Yorker. It gets a little hazy about where the investigation went next, but the indictment against Manafort lists several properties identified by the team. The trio can neither confirm nor deny whether they've been contacted by a certain investigation led by Robert "Future Robert De Niro Academy-Award-Winning Role" Mueller.