While we doubt the veracity of this man's police report (if he was robbed by ninjas, how would he know?), we want to believe in it for one reason: the existence of stoner ninjas. Though wouldn't the art of ninja'ing be inhibited by marijuana? We imagine it would be harder to hide in the shadows when your paranoid mind is shouting "Dude they can totally see you, they know, they know, they know!" 

Sources: San Gabriel Valley Tribune