John 19:30ff

Sometimes it would take 2-3 days for a person to die on a cross... to move the process along, soldiers overseeing crucifixions, would break the legs of victims. This meant they could no longer attempt to hold themselves up...thus fatally slumping that lead to suffocation. The Jewish leaders were impatient for this to be over, and sought a quick solution. The two criminals on either side of Jesus, die after their legs are snapped.  But when the executioners come to Jesus, they find him already deceased. So instead of breaking bones they thrust a spear in his side. Hundreds of years before, the Old Testament predicted that none of his bones would be broken, yet his side would be pierced. Indeed this was the promised, Messiah, the Son of God.