Source: Washington Monthly - Link
Thompson is suing under a seldom-used section of the Ku Klux Klan Act. The sweeping civil rights statute was passed in 1871 while the Grant administration was trying to control racial terror in the post-Civil War South. One seldom-used section may offer a clear shot at new evidence, and eventually a trial for those involved, actively or passively, in the attack.
Interesting tack Thompson is taking. It just might work.