so far, it appears the attacker was working alone but tonight, paris is on edge and abc's john longman leads us off from the scene. >> reporter: panic today in the heart of paris, throngs of tourists sent running, as shots ring out in front of one of the world's most iconic cathedrals. the drama began at 4:20 p.m., surveillance cameras trained on the crowded plaza in front of notre-dame capture the moment an attacker lunges at three police officers, striking one of them with a hammer. one of the other officers draws his gun and fires. the attacker falls to the ground. you can see the man lying on the ground here, an officer standing over him, the cellphone video recorded by an american tourist, kyle riches. >> we heard two gunshots and so at that point, my wife and i ran away to the corner, and then we turned around and saw a guy on the ground who was bleeding. >> reporter: as police rushed to the scene, frightened tourists scatter. >> you didn't know what was happening, people running towards us, so you have to keep running. >> reporter: inside the ancient cathedral fear and confusion