A 20-year-old U.S. citizen's Twitter posts sympathizing with Islamic terrorists led to an undercover FBI operation and the man's arrest on charges that he plotted to blow up the U.S. Capitol and kill government officials. Christopher Lee Cornell, also known as Raheel Mahrus Ubaydah, told an FBI informant showed his plans for bombing the Capitol and shooting people, according to a criminal complaint filed in federal court in Ohio Wednesday. The FBI said Cornell expressed his support for the Islamic State and al-Sham (ISIS). Cornell was arrested Wednesday after buying two semi-automatic rifles and about 600 rounds of ammunition, authorities said.Cornell's arrest came only days after a grand jury indictment charged another Cincinnati-area resident with threatening to murder House of Representatives Speaker John Boehner. Boehner spokesman Michael Steel said in a statement Wednesday: "Once again, the entire Congress owes a debt of gratitude to the FBI and all those who keep us safe." The complaint against Cornell charges him with attempting to kill officers and employees of the United States.Cornell planned for the two to detonate pipe bombs at and near the Capitol and then shoot and kill employees and officials, and Cornell had saved money to fund the attack, according to the complaint.