"He was out the building." "He was into the building."
The first one looks good. The second one seems suspect. Could the second one be okay after all?
" "He was into the building."
You use into normally with verbs of movements (run, go, walk, jump etc...) to indicate movement from the outside to the inside of a building or an environment.
He ran into the living room
He jumped into the water.
Normally BE is never followed by into except as a phrasal verb and its meaning totally changes then.
He is in the office. She is in the kitchen and so on...
I hope it helps