Security expert Fred Burton, a former Secret Service officer and special agent with the U.S. Diplomatic Security Service, told Newsweek that there were “many unknowns” around Saturday’s incident, including whether the suspect was previously known to the agency.

Burton said that the evacuation of officials and the response by the Secret Service’s Counter Assault Team was “spot on,” but described the “tempo of attacks” on the president as “highly troubling.”

He added that, going forward, the agency would likely station officers ahead of magnetometers—which the suspect was able to run through—and consider deploying additional security dog teams.