Aidan Becker was stabbed to death while trying to protect a schoolboy at a train station. (Jay Kogler/AAP PHOTOS)Aidan Becker was stabbed to death while trying to protect a schoolboy at a train station. (Jay Kogler/AAP PHOTOS) Credit: AAPThree teens accused of killing a man who was trying to protect a schoolboy from a robbery have been committed to stand trial. Mr Becker, an off-duty security guard, was fatally stabbed at Mernda train station on Melbourne's northern outskirts on March 6. The parents of the schoolboy Mr Becker was protecting also paid tribute, saying he showed extraordinary courage and compassion to save their son.