From the window of my former workplace I could see down onto a flat roof that was regularly visited by a couple of magpies and a crow.
I bought nuts and threw a handful of them daily onto the roof to watch them eat. It was very obvious that they didn't trust me at all.
If you made it obvious that you were watching them they wouldn't go get the nuts closest to the window. The was still several meters, a closed window, and another building away so there would have been no possibility for me to catch them.
I always had to act like I was not watching the roof until they tried to get the nuts. Also it got a little better even after a year of doing this they still did not trust me at all.
Also crows are like raccoons in the way that they like to wash their food. Sometimes there was a puddle on the roof after it rained and the crow came there regularly with something to eat to wash it in there beforehand.