According to what I've read, an army went out to a specified point. At that time, the 800 soldiers and laborers went out. The soldiers camped and waited for the laborers who went out and performed the buriel at a spot unknown to the soldiers. The laborers returned to the 800 soldiers, not knowing the soldiers had orders to murder them all, so Khan's whereabouts would not be known. When the soldiers returned to the main army, they were murdered, in case any of the laborers had revealed the whereabouts of the tomb to save his life. The 800 returning soldiers did not know that they were going to be murdered either. It's been a few years since I read the account, so some other Freeps may be able to clear up any errors I made, but this is basically the account.
I've read the same or similar story.