The U.S. Capitol Police have launched an investigation into whether an elite tactical team was abruptly recalled from responding to [the] Navy Yard shooting massacre before D.C. Metropolitan Police officers confronted the shooter. Two Metropolitan Police officers entered the Navy Yard without the Capitol Police team and one was wounded by the gunman, Aaron Alexis. The elite Capitol Police Containment & Emergency Response Team [CERT] is based just a few blocks from the Navy Yard. A law enforcement source told WUSA-TV the unit was less than 30 seconds from the gate and responded as Metropolitan Police pleaded for help. A Capitol Police watch commander wouldn't let them go in and stop people from being slaughtered," one officer told the Washington TV station. An officer told The Washington Post that the officers' union had filed a complaint. The Capitol Police have launched an investigation into the allegation "We were definitely the closest tactical team in the city," the unidentified officer told the newspaper. "[The team] was at the scene very early on, within a couple of minutes. They were ordered to disengage and turn back. For what reason, we don't know." The CERT, created in 1978, consists of three "cells" - two assault teams of at least six officers each, plus and a counter-sniper unit. Two teams were on duty [at the time of the shooting incident].