In the professional opinion of the Roman soldier on site, Jesus was dead. He had suffocated from crucifixion, a particularly nasty way to die. The stress of suffocating after the day of beatings, getting dragged from court to court, and carrying the heavy crossbeam of the cross is almost unimaginable. Breaking the legs of those executed by crucifixion accelerated their dying. When hanging from their hands, victims were unable to exhale, they would stand, draw breath, and collapse again until starvation for air forced them up, aggravating the wounds in their feet where they were nailed to the cross. Broken legs meant no standing up, so the prisoners would be suffocated within minutes.
Jesus requires no such assistance, as I said, in the professional opinion of a soldier, He was dead. Just to be sure, they drove a spear into His side. The accumulated fluid in his lungs spilled out as water. The membrane around the heart, the pericardium, was full of blood from His burst heart. As the blood and water flowed down the spear there was proof enough for religious leaders and governors who had never seen death on the battlefield.
Not only were the enemies of Christ convinced He was dead, but His friends were as well. Joseph and Nicodemus were followers of Jesus, friends who used their social position to acquire the body. They made Jesus ready for burial according to the customs of the time, which required no few hours of manipulating, washing, and wrapping the corpse. If there had been any sign of life, would these loving friends have missed it? Then they lay Jesus in a tomb cut into the rock on a spring night in Jerusalem. Had some spark of life remained by impossible chance it would have extinguished in the quiet of the cold tomb with no water, no food, and hypothermia. Jesus really died.