All of the crimes he did commit happened before the campaign and none of them had to do with Russia.
As Fox News Reports:
In June 2018, Mueller’s team brought additional charges of obstruction of justice against Manafort and Konstantin Kilimnik, an associate.
The charges against Manafort and Gates don’t relate to allegations of misconduct during Trump’s campaign.
Mueller also accused Manafort of secretly paying former European politicians to lobby on behalf of Ukraine.
Manafort has maintained his innocence despite all of the charges brought before him.