Authority? Josephus? or what?
Pontius Pilate.
Remember that he was surprised that Jesus died so soon. The piercing of His side was simply a way to ensure to Pilate that He was dead before the Sabbath so that He could be taken down and buried according to the pleas of His followers.
Tsk, tsk. Must read that Bible of yours, mustn't you? :)
We do not know here from Pontius Pilate. We don't know "days." We only know that he shortened the malefactor's legs to shorten their hours so they couldn't raise up to breathe. They died from pulmonary edema, congestion of the heart. It would take some other historical account to give us the confidence that it took days, rather than hours.
Are you only relying on one book here? I am not, in this matter.
Jesus died by Himself giving up his spirit to God. His body went to the grave, and His soul to Paradise to preach to the OT saints there. Jesus knew, by foreknowledge, that one of the malefactors would be there, too, with Him.