ABC's Andy Field returned to KRDO's Afternoon News as the president of the United States has been permanently banned from posting on a social media platform "due to the risk of further incitement of violence," and the U.S. attorney's office in D.C. has opened a federal murder investigation into the death of U.S. Capitol Police officer Brian Sicknick, who died Thursday night after suffering injuries in the violent siege at the Capitol, three law enforcement sources confirmed to ABC News.  The investigation is being conducted jointly between the FBI and the D.C. Metropolitan Police Department, with cooperation from U.S. Capitol Police. Acting Attorney General Jeffrey Rosen said in a statement, "The Department of Justice will spare no resources in investigating and holding accountable those responsible.”