(CNN) For months, 20-year-old Christopher Lee Cornell had been on the FBI's radar. Authorities said he left alarming posts on social media, talking about violent jihad. On Wednesday, agents arrested the Cincinnati, Ohio, man before he could put his alleged plot into action. Authorities say Cornell, who ostensibly tweeted under the name Raheel Mahrus Ubaydah, hatched a simple scheme. It was similar to the Paris attack on the offices of Charlie Hebdo, but at a key location -- the U.S. Capitol, said a criminal complaint filed by an FBI agent. The plan: Set off pipe bombs to put lawmakers and...