The Head That Lived

[Mysterious Benefactor]

In that case Desmond wouldn't have had to find the old man (I forget his name) who had had the Head a long time before and who died in Desmond's room.  The Head clearly didn't know where the body was and was using Desmond to find it.

Oh, that's right (see what happens when you haven't watched these episodes in years ). But be that as it may, it still holds true that the head could have imparted the whereabouts of the vault to Leticia while she had it in her room.