Before being crucified, Jesus was whipped to a point of near death.
• …Roman scourging often caused death before crucifixion.1
• …the Gospel report it explicitly (Mt 27:26, Jn 19:1).
• …he was consequently incapable of carring his crossbar.2
All victims of crucifixion die.1
• …our abundant records of crucifixion unanimously end in death.
• …death follows even partial-crucifixion.2
The presiding Roman Centurian felt certain that Jesus was dead, as did the other soldiers (see Mk 15:24).
• …Roman executioners ensure death professionally.
• …the Centurion assured Pilate that Jesus was dead.
A Roman soldier speared Jesus in the side to ensure that he was dead.1 (Moreover, “blood and water came out,”2 a symptom of one of two conditions that requires the patient be dead.)3
Everyone from AD 30 onward persisted in believing that Jesus had died by crucifixion. This should be granted because sources from AD 30 onwards reported Jesus's death. Notably,
• It was reported in the New Testament (The gospels, Paul's letters etc.).1
• It was reported in non-canonical Christan sources,
• It was reported in non-Christian sources. [Forthcoming]
Everyone involved in taking down Jesus's corpse, wrapping, and burying it felt that Jesus's body went lifeless (no breathing etc.). This is relevant because, if Jesus was still alive, the individuals handling and carrying Jesus's corpse would have inevitably heard/felt/saw Jesus breathing, pumping blood etc.
Victims of crucifixion rarely die within three hours (i.e. when Jesus was taken down).
• We know that crucifixion commonly lasted for days.1 So, naturally,
• Mk 15:44 -- “Pilate was surprised to hear that he was already dead. Summoning the centurion, he asked him if Jesus had already died.”
But, so what? Jesus was scouraged nearly to death beforehand.2
See: Was Jesus crucified?