"Barn Where Assassin Was Concealed"

I don't recall seeing a picture before of this "barn where assassin was concealed." I assume it was on the Steunenberg property, being "some 300 feet distant," but could be wrong in that regard. And whose house is that in the background? Is it a still existing neighborhood home? If any one can shed some light on this photo then please let me know. Click images to enlarge.............................. (cont. from above)