This is interesting for a few reasons.Air Marshalls are specially trained officers who fly in plainclothes on regular rights, mostly to be ready to intervene during a hijacking, etc. They are not normally part of this sort of criminal investigation, except in very special cirucmstances.
I assume shoulder surfing passwords is a fairly specialized skill to do well. Are air marshals routinely trained to do this? If so, it suggests they have rather different role than we've been led to believe.