( CNN ) -- A traffic snarl outside Washington 's Navy Yard -- not a tactical command decision -- prevented a special U.S. Capitol Police unit from responding at the scene of a mass shooting there in September , an internal police report found on Friday . Twelve people were killed in the September 16 rampage by gunman Aaron Alexis , who was also killed during a shootout with other law enforcement officers . The deployment disclosure came after some initial media reports said the Containment Emergency Response Team was one of the first on the ongoing shooting scene , then turned away at the command center , and subsequently pulled back . `` Initial reports of the actions of USCP personnel were inaccurate and failed to convey the nuanced complexity of such situations including the personal and professional impact on potential first responders , '' said a summary of the report by the U.S. Capitol Police Board . The shooting at the Navy Yard facility several blocks south of the U.S. Capitol complex attracted a number of law enforcement , including some Capitol Police officers who `` self-deployed . '' The board 's review team interviewed dozens of Capitol Police officers and examined written reports , radio transmissions , and command center incident logs . The report did not deal with actions taken by other federal and local law enforcement , including military police officers . Following some initial reports about the CERT 's deployment , the local police union at the time had urged an investigation into the team 's actions and orders . `` They were prepared to risk their lives to save the lives of the shooter 's victims , but were prevented from doing so , '' labor committee Chairman James Konczos said in a statement a week after the shooting . `` It is impossible to say how the outcome would have been different if the CERT team had been permitted to respond . '' Capitol Police Chief Kim Dine then ordered the police board review team to look into the allegations the special response team was diverted from the shooting scene . `` Because of traffic gridlock caused by both emergency vehicles and commuter traffic the CERT unit was unable to reach that incident command post , '' said the report . `` The CERT unit then moved closer to the Capitol , increasing its flexibility to respond as needed at either the Capitol or the Navy Yard . '' Officials had said there was initial concern the Capitol might become a secondary target , promoting an increased security presence there . CNN 's Paul Courson , Carol , Cratty and Joe Johns contributed to this report .
There were suggestions the U.S. Capitol Police special response unit was diverted . But internal police report said that was inaccurate . Snarl of emergency vehicles , commuter traffic actually prevented the unit from the reaching scene . Comment: