terror take-down in boston. grainy surveillance video showing confrontation between suspect usuma rahim and anti-terrorist agents. rahim s family says the video reveals part of the story. abc s tom llamas reports. reporter: this is the moment five fbi agents and boston police officer approached the terror suspect, usama rahim. watch closely as officers back away. rahim, seen circled in yellow coming toward them. you can then see two officers move toward him. rahim goes down. police say the two anti-terror agents shot rahim though you can t see it in the video he was arm ed with the large knife and allegedly threatened to kill police officers. there are questions asked why didn t the officers use any other force? you know this guy had a malicious intent and our officers were really faced with that. reporter: they approached him because the fbi listening in on his cell phone conversations allegedly heard him say he was about to go after the boys in blue. we intercepted a communic