The moment Jesus’ body was laid in the tomb and the sun set and darkness began to invade the land. (Because a Jewish day begins at night when the first stars come out.) The Chief Priest and Pharisees went back to Pilot to make sure Jesus’ body stayed in the tomb. I wouldn’t be surprised if they had someone hiding in the bushes at the tomb watching it until the Roman Garrison got there. The last thing they wanted was to hear that Jesus had rose from the dead, because His body was no longer in the tomb.
… with in moments of Jesus being laid to rest, they showed up with Roman Soldiers and sealed the tomb. Once that was done they rested. They had a sigh of relief that He was finally gone and there was no way the Disciples could steal the body because the Roman Soldiers were guarding the tomb and even if there was a squirmish word would get out an the rest of the garrison that was in the city would hunt down the Disciples and put them to death. Because, to attack Roman Soldiers would be an act of war.
It’s not that they believed Jesus.
It’s they believed his followers were dumb enough too and that made them dangerous.
However, the danger for these Scribes and Pharisees was never the Disciples. Their danger was unbelief in the One who just died for their sins and they were already living “smack dab” in the middle of that dangerous world.