Albert Barnes Commentary Mark 15:44

"And Pilate marvelled if he were already dead: and calling unto him the centurion, he asked him whether he had been any while dead." — Mark 15:44 (ASV)

And Pilate wondered if, etc. Wondered if he was dead, or wondered that he was so soon dead. It was not common for persons crucified to expire under two or three days, sometimes not until the sixth or seventh.

Joseph had asked for the body, implying that he was dead. That he was had been ascertained by the soldiers. See John 19:33.