Yes they did. But they didn't put him on trial, did they? But for example it's taken California 3 and a half years to start Robert Blake's trial. The wheels of justice grind slowly sometimes, and in the case of Jefferson Davis he should be glad that they do.
As OJ proved, Blake had the right to a speedy trial. Delay was at Blake's request. In Davis the accused announced in court that he was ready to proceed and the government, after more than two years, announced that it was still not ready to proceed. In point of fact, the government was never ready to proceed in the Davis case.