I keep a file on my Dropbox titled "Where Are They Now?" for exactly this purpose. Whenever I get curious about this sort of thing I add their name, a brief description, and the date to a list.

I don't just do it for "bad" people, but for all sorts of people that become notable for one reason or another. For example I (somewhat) recently added David Hogg & Emma González to the file.

I'm hoping that it will prove to be interesting reading in 10-20 years.