Death by crucifixion was meant to be slow and painful. Ultimately, one died by suffication. In a crucified position, a human can only breathe by pushing the diaphram out and this can only happen by pulling up with one's arms or pushing up with one's legs. This becomes increasingly exhausting over time: eventually one become so exhausted that one can no longer pull up or push up. In order to hasten death, sometimes the legs of those crucified were intentionlly broken so that the person would not be able to use the legs to push up.
JH 19: 31-34 "The the Jewish authorities asked Pilate to allow them to break the legs of the men who had been crucified, and to take the bodies down from the corsses. They requested this because it was Friday, and they did not want the bodies to stay on the crosses on the Sabbath, since the coming Sabbath was especially holy. So the soldiers went and broke the legs of the first man and then of the other man who had been crucified with Jesus. But when they came to Jesus, they saw that he was already dead, so they did not break his legs. One of the soldiers, however, plunged his spear into Jesus' side, and at once blood and water poured out."
Comment: Notice how the death of Jesus becomes rushed: everything is hurry, hurry. A Jewish holiday begins a sunset the evening before. To be ritual pure for this religious feast, the Jews could not be handling a dead body. Jesus must be dead and buried before sunset.