They asked for a watch and Pilate told them they had one. This is easily translated that he gave them one and told them with a wave of the hand to get out of his face and use it as they had requested.
Later in Matthew (28:14) the elders promise those on the watch that they will persuade the governor (Pilate) and "secure you". Now why would the tomb guards be afraid of Pilate if they actually belonged to the Jewish religious authorities who were promising to protect them?
IMO, this isn't quite right:)
The only place I find the "guard" talked about is in Matt. 27:62-66. I read it as Pilate did give the Jewish people a detail of guards and told them to make it as secure as possible.
But even if (which I don't think) it was the Jews guarding it, they would be as diligent at keeping it safe as the Romans, they didn't want a resurection to take place anymore then Rome did.
Becky