He was to be absent for an undetermined period, but at least three weeks.

His disappearance would occasion no comment; his absence would lead to no inquiries, at least for several weeks, during which the murderer would have leisure quietly to dispose of the body and conceal all traces of the crime.

The conditions were, from a murderer's point of view, ideal.
"But that was not all.

During that very period of John Bellingham's absence Mr.Jellicoe was engaged to deliver to the British Museum what was admittedly a dead human body; and that body was to be enclosed in a sealed case.

Could any more perfect or secure method of disposing of a body be devised by the most ingenious murderer?
The plan would have had only one weak point: the mummy would be known to have left Queen Square _after_ the disappearance of John Bellingham, and suspicion might in the end have arisen.