Good question. I'd never really thought of that before, but it makes sense. Margaret sat in the same seat that Leslie did, a piece of evidence Columbo could have deduced from the angle of the bullet entry (assuming the remains allowed that kind of deduction).

Did he give her the plane transponder, too?

i am also wondering who confronted her with the plane trasponder/beacon and how it was found.
i guess it's obvious columbo gave it to margret for shock value.

this scene would work great as a nightware sequence, if the killer had any remorse.