Did Robert Lincoln Ride the Funeral Train to Baltimore?

[Eva Elisabeth]

I wonder why RTL gave him the vault keys instead of keeping them himself?

Since Robert was about to live in Chicago I suppose he left the key in Springfield in case something happens that requires immediate access (e.g. a fire). Plus J.T.S. wasn't only a relative but also a lawyer and would know what cases would justify to use it.

Another reason - the key was in Springfield at any time a close friend or relative came to visit the grave.