Yes, if and only if there was hard evidence they were innocent. If the evidence isn't clear or substantial enough, too bad.
Rin-chan
According to my dictionary clemency means mercy or leniency. In that case we think the person is guilty but we go easy on him for one reason or another. On the other hand, if there is new evidence which suggests the person is innocent then I would give a temporary reprieve pending a new trial, or if the evidence is conclusive that he is innocent I would grant him a full pardon absolving him of all guilt, restoring his rights and releasing him immediately.