A murder occurs in a nursing home during a night full of thunderstorms and pouring rain. The victim is discovered lying on the plush carpet of the rec room, bleeding from a wound to the head. The staff assures investigators that there must have been a break-in because no one who lived or worked at the facility would do something like that. Considering the Principles of Trace Evidence, what would investigators be looking for to prove that someone entered from outside the facility?

Muddy or wet footprints in the carpet
The discovery of a murder weapon
Letters to the victim from a sick relative
Blood spatter from the victim's head wound