Well, just going by Tom's incorrect assessment that it would be virtually impossible to get close enough to Roth to kill him.
It may have appeared quite simple for Rocco to be posing as a reporter, but the unseen logistics/timing of getting to that point while armed may have been a bit more complicated. Or shall I say...'difficult'.
Apple
I think it was Tom's unspoken qualification that the assault was impossible if one intended that the assailant would get away.
