What crime was committed by the "thieves" crucified with Jesus?

During yesterday's sermon, the pastor mentioned the theory that the thieves crucified next to Jesus likely weren't simple thieves to warrant such a sentence, but were probably "thieves with a cause." He suggested today they would likely have been considered religious or political zealots, or "terrorists." The pastor's suggestion seems a *little* far-fetched to me, based on how the thieves responded to Jesus: One mocking him, the other asking pardon. These don't seem like the sorts of attitudes that religious or political zealots sentenced to death are likely to exhibit. I would expect "terrorists" to more closely identify with their cause. Do we have enough information, historically or textually, to draw any conclusions about these thieves' crimes? Was crucifixion used to punish "simple thieves?"