Was Pilate mandated to withhold the body of Jesus after the Crucifixion?
The short answer is no. He had the authority to release the body of Jesus to his family, but only after verifying that Christ was indeed dead.
But by Roman tradition, Romans left the bodies on the Cross for the animals to be devoured by wild animals and birds of prey. Notwithstanding, Pilate, as Governor of Judea, has the authority to release the bodies of those condemned to Crucifixion.
As one of the main objectives of this cruel method of execution was its deterrent value, Roman authorities also devised various means whereby the victim could remain on the cross for days in public before eventually expiring. Thus the manner in which the victims were crucified was not fixed by law but appears dependent on the number of individuals involved, the sadistic ingenuity of those carrying out the execution and the time needed for this spectacle to have its maximum deterrent effect.
Giving the victim a proper burial following death on the cross, during the Roman period was rare and in most cases simply not permitted in order to continue the humiliation. Thus the victim was in many cases simply thrown on the garbage dump of the city or left on the cross as food for wild beasts and birds of prey. - Crucifixion in Antiquity- The Evidence
Let us see what the Sacred Scriptures say about Jesus’ death.
Afterward, Joseph of Arimathea, who was a disciple of Jesus (but secretly for fear of the Jews), asked Pilate to let him remove the body of Jesus. Pilate gave him permission, so he came and removed His body. - John 19:38
St. John goes on to explain the conditions surrounding Jesus’ descent from the Cross.
31 Now it was the day of Preparation, and the next day was to be a special Sabbath. Because the Jewish leaders did not want the bodies left on the crosses during the Sabbath, they asked Pilate to have the legs broken and the bodies taken down. 32 The soldiers therefore came and broke the legs of the first man who had been crucified with Jesus, and then those of the other. 33 But when they came to Jesus and found that he was already dead, they did not break his legs. 34 Instead, one of the soldiers pierced Jesus’ side with a spear, bringing a sudden flow of blood and water. 35 The man who saw it has given testimony, and his testimony is true. He knows that he tells the truth, and he testifies so that you also may believe. 36 These things happened so that the scripture would be fulfilled: “Not one of his bones will be broken,” 37 and, as another scripture says, “They will look on the one they have pierced.”
38 Later, Joseph of Arimathea asked Pilate for the body of Jesus. Now Joseph was a disciple of Jesus, but secretly because he feared the Jewish leaders. With Pilate’s permission, he came and took the body away. 39 He was accompanied by Nicodemus, the man who earlier had visited Jesus at night. Nicodemus brought a mixture of myrrh and aloes, about seventy-five pounds.[e] 40 Taking Jesus’ body, the two of them wrapped it, with the spices, in strips of linen. This was in accordance with Jewish burial customs. 41 At the place where Jesus was crucified, there was a garden, and in the garden a new tomb, in which no one had ever been laid. 42 Because it was the Jewish day of Preparation and since the tomb was nearby, they laid Jesus there. - John 19:32-42
When the Romans saw that Jesus was already dead “one of the soldiers pierced Jesus’ side with a spear, bringing a sudden flow of blood and water.”
This piercing of the side of a Crucified, is know as the “coup de grace” which in French means to deal a deathly blow for the purpose of ending suffering. The ultimate coup de grace took place when God chose to wipe out all of our sin in a single blow — and in doing so, bridged the gap for us to have a new life in Him. When Jesus died on the cross, He offered a death blow to our sinful nature forever.
When victims were permitted to taken down from the cross, the Roman Centurion had to make sure that the person was nor walking away with life still in him. Historically a few victims were handed over to their families but only after the proofs of death were assured. The executioners were not medical professionals and thus their brutally could be seen in hastening and in verifying death!
By Roman law, the family of the condemned could take the body for burial, after obtaining permission from the Roman judge.
Since no one was intended to survive crucifixion, the body was not released to the family until the soldiers were sure that the victim was dead. By custom, one of the Roman guards would pierce the body with a sword or lance. Traditionally, this had been considered a spear wound to the heart through the right side of the chest—a fatal wound probably taught to most Roman soldiers. Moreover, the standard infantry spear, which was 5 to 6 ft (1.5 to 1.8 m) long could easily have reached the chest of a man crucified on the customary low cross. - Scourging and Crucifixion In Roman Tradition