A conviction is not required before suing someone civilly. However, if someone is convicted of a crime and there is also a civil cause of action, the plaintiff wins automatically with only damages to be determined.
As a practical matter, how far do you think the plaintiff(s) would get without a criminal conviction? I can think of OJ, but not many other instances. In that case, too, it was a handy change of venue. Regrettably, venue more than the law determines the verdict. IMAGINE suing an Obama Administration official in the DC federal court. ha!