I would say that, technically, the executor is only entitled to look at the estate as at date of death and from then on BUT if he is on notice that there were extraordinary movements on the account, in the months leading up to the death, such as would give rise to a presumption that someone was "stealing" and, if this has the effect of reducing the estate, and the monies available to beneficiaries, then that changes the picture.
Much depends on the size and complexity of the estate. And perhaps the intrusive nature of unnecesary enquiries ( some executors can lose the run of themselves).
As with most things, it depends.
mf