They shouldn't "pardon". If there were some other form of nullification, that might be ok, but did nothing wrong by modern standards, and "forgiving" him implies that he did, even if that isn't their intent. And any legal relief a pardon would give a living person is irrelevant.
Let the conviction stand as a historical marker of shame.
Instead, they should vote on an apology to him and all the other people wronged by the actions of their predecessors.
> but did nothing wrong by modern standards, and "forgiving" him implies that he did
One of the purposes of the pardon power is to nullify convictions where a law was broken but the conviction, justified as it might be by the law, was unjust in the specific context.
Now, its designed (on the premise that the law is always just in the general case) to deal with exceptional cases, but it is no less appropriate a vehicle for the case where the law failed to be just in general and thus any conviction under the law is unjust in its specific context.
Let the conviction stand as a historical marker of shame.
Instead, they should vote on an apology to him and all the other people wronged by the actions of their predecessors.