evidence: As the investigation into the assassination attempt on former President Donald Trump intensified Sunday, the U.S. Secret Service was coming under scrutiny as questions mounted on how the alleged gunman managed to fire a barrage of shots from a rooftop with a vantage point of the outdoor Pennsylvania rally stage Trump was speaking from. [...] Watch the ABC News special, "Trump Assassination Attempt Minute by Minute," Sunday at 8 p.m. ET [...] Xochitl Hinojosa, spokesperson for the Department of Justice, said in a statement Sunday that Attorney General Merrick Garland has canceled plans to travel to Nevada, Utah and Kansas this week to meet with local law enforcement and speak at the National Bar Association. Hinojosa said Garland will stay in Washington, D.C., to closely monitor the investigation of the attempt on Trump's life.