Who could have watched the veil of the temple tear when Jesus died?

A professor today made the claim that the following claim is spurious: > And the curtain of the temple was torn in two, from top to bottom. Mark 15:38 (NRSV) His rationale is that no-one but the high priest would be allowed to see the veil in the holy of holies in the temple, so the author of Mark could not have knowledge of such an event occurring. Is this claim accurate? Who would have seen or had knowledge of the tearing of the veil that could have communicated that event, directly or indirectly, to Mark? How could this event have made it to Mark?