I believe he was beaten and robbed of his wallet and briefcase resulting in his confusion - may have a resulting head injury or even been drugged.
Also, if you look closely at his jacket you can see the left sleeve is dirty as are his pants like he was thrown to the ground.
The fact that he was robbed on one day and killed the next is more than coincidence.
Wasn't there snow on the ground? Is I fall down in the snow there is not dirt on my clothes but snow which just melts and leaves a wet spot that dries. Only if he falls in an area where there is loose ground or mud will it adhere to the cloths and stay there when dry. So where did his clothes come into contact with dirt? And won't the FBI labs be able to tell by matching exactly where that location was?