Actually from a Jewish perspective, may I add that our history is clear that the Romans used crucifixion any damn way the pleased.
While Jesus may be the most famous Jew ever crucified, he was definitely not the only one. Many Jews were put to death in this agonizing fashion. While crucifixion was officially reserved for crimes which required capital punishment, this was not always the case unfortunately. Romans were no different from people of today who bend the rules and allow power to go to their heads to the point of abusing it and the people under them.
While I don't believe Jesus was the Messiah, of course, as a Jew I can attest that the details of the crucifixion attributed to this case do suggest he was crucified with theives. The fact that an order to break their legs due to the coming Passover is something that implies a good knowledge of what crucifixion both does and why breaking legs was necessary before the Passover.
The cross had a tiny footrest of sorts (sometimes the legs were just slightly bent at the knees instead) in order to agonizingly delay death by asphyxiation. Not being able to fully stand made the lungs fill and the person slowly drowned in their own bodily fluids. If they could fully stand and bring their arms in, they could stop this process and recover, but since they were nailed in this position with their arms outstretched it became impossible. Death could take days.
But since Rome recognized Judaism as an official relgion of the state, crucifixions in the vicinity of the Temple in Jerusalem had to be cut short when a Sabbath or other holy day approached. The Law forbid hanging people on a Sabbath. Romans had learned that by breaking the legs the lungs would instantly flood with bodily fluids and blood and the person would basically drown. So when something like the Passover arrived, the Romans were all too happy to oblige to clear away the crucified in this way as they were equally satisfied to watch the horrific struggle for air that would follow.
It is also a peculiar note that the Gospels report that upon using a spear to determine if Jesus was dead that water and blood are spoken of as being released. (John 19.34) This suggests that the lung was pierced, and this is at least consistent with what is to be expected from death by crucifixion.