Secret Service reportedly flagged Donald Trump's would-be assassin as suspicious before he took aim at the former president.
The 78-year-old ex-president hosted a rally in Butler, Pennsylvania, on July 13 that ended in deadly chaos.
A gunman identified as Thomas Matthew Crooks, 20, opened fire at the event, leaving Trump with an ear injury after he was grazed by a bullet that flew past his head.
One victim named Corey Comperatore was killed, while two other victims, 57-year-old David Dutch, and 74-year-old James Copenhaver were both shot and are now in stable condition.
Footage shared online shows the Republican nominee speaking to the crowd when several armed security forces jumped onto the podium to protect him from the bullets.
The shooter was killed by Secret Service snipers within 26 seconds of opening fire, as reported by BBC.
The Secret Service has faced scrutiny over security failures that led to the shooting at the rally.
According to reports, the suspected shooter was spotted early by police, who notified the Secret Service via radio that a "skinny young man" was behaving suspiciously. They lost him in the crowd before he was spotted again by the counter sniper.
“He was identified as a character of suspicion because [he had] a rangefinder as well as a backpack. And this was over an hour before the shooting actually occurred,” Wyoming Senator John Barrasso, who was present at the briefings, said.
“So, you would think over the course of that hour, you shouldn’t lose sight of the individual," he added.
Per the BBC, Crooks was spotted again at around 17:45 local time by a counter-sniper officer around the Agr International building, which is where he was when he aimed at Trump.
An unnamed official snapped a photo of the suspect looking through the rangefinder - an instrument that helps measure the distance to a target - and immediately informed a command post to report the sighting.
By 17:52, which was 19 minutes before the shooting, the SS was made aware that Crooks was spotted with a rangefinder and conveyed that information to other officers on site.
Several senators have criticized the lack of honesty from investigators and demanded the resignation of Secret Service Director Kimberly Cheatle after the revelation.
"I am appalled to learn that the Secret Service knew about a threat prior to President Trump walking on stage," Senator Marsha Blackburn of Tennessee tweeted.
"The egregious security failures and lack of transparency around the assassination attempt on President Trump demand an immediate change of leadership at the Secret Service," Utah Senator Mike Lee chimed in.
Senate Minority Leader Mitch McConnell added that "the nation deserves answers and accountability" and a change in leadership at the Secret Service would be "an important step in that direction".
Meanwhile, Trump gave his first speech after his terrifying near-death experience, saying that it's a miracle he's still alive.
"The amazing thing is that prior to the shot, if I had not moved my head at that very last instant, the assassin’s bullet would have perfectly hit its mark, and I would not be here tonight," he said.
"None of us knows God’s plan, or where life’s adventure will take us. But if the events of last Saturday make anything clear, it is that every single moment we have on earth is a gift from God. We have to make the most of every day for the people and country we love," he added.