"Many people jumped and I witnessed it, I watched that. I have a view -- a view in my apartment that was specifically aimed at the World Trade Center," Trump said Monday during a rally in Columbus, Ohio.
"And I watched those people jump and I watched the second plane hit ... I saw the second plane hit the building and I said, 'Wow that's unbelievable,'" Trump continued.
At least 200 people are believed to have jumped from the Twin Towers after planes struck the towers in an attack that claimed more than 2,600 lives.
The Republican presidential contender lives in Trump Tower in midtown Manhattan, more than four miles away from where the World Trade Center towers once stood. Trump has lived in the 5th Avenue tower since before the attacks, according to media reports pre-dating 9/11.
The Trump campaign did not immediately respond to a request for comment asking how Trump witnessed people jumping out of the Twin Towers from more than four miles away.
Trump on Monday also dug into his claim that Muslims in New Jersey celebrated the terrorist attacks on 9/11, a claim that has been widely debunked by multiple fact-checkers.
Ben Carson, a rival Republican presidential candidate, initially backed Trump's claim about American Muslims celebrating the terrorist attacks. But on Monday his campaign walked back Carson's statement.
"Dr. Carson does not stand behind the statement attributed to him early today regarding events surrounding 9/11. He does not believe Muslim Americans in New Jersey were celebrating the fall of the Twin Towers," Carson communications director Doug Watts said Monday in a statement.
In a classic stump speech Monday, Trump captivated a crowd of supporters by talking up his front-runner standing in the latest polls, mocking Ohio Gov. John Kasich's bottom-tier poll numbers, and slamming the press for covering a violent altercation at his previous rally between a Black Lives Matter protester and several white attendees.
Several hecklers at Monday's event were escorted out by police, and audible boos could be heard in the crowd during parts of his speech.
But Trump's biggest applause lines came when he talked up his positions on combating terrorism.
After touting his strong approval numbers in recent polls on how he would handle the economy and lead the country, Trump stated that voters also "love him on terrorism," to which the crowd erupted in applause.
Trump later played up his support for waterboarding, drawing cheers from the crowd.
"Would I approve waterboarding? You bet your ass I would," the candidate said of the practice, which is considered torture under international conventions.
President George W. Bush authorized the interrogation technique under his administration, a practice President Barack Obama condemned and officially ended when he entered office.
Critics contend the practice has been proven unreliable and largely ineffective compared to standard interrogation techniques.
But Trump insisted that the approach gets results: "Don't kid yourselves folks, it works."
The brash billionaire also didn't back down from his controversial comments that he would consider shutting down mosques or putting Islamic houses of worship in the U.S. under surveillance to guard against future terror attacks.
"We have great people in the Muslim population, but something's happening. Something's happening. I always say they're not coming from Sweden that want to kill us, they're not coming from Norway, they're not coming from Denmark. They're coming from a certain part of the world with a certain philosophy," Trump said. "We have to have strong surveillance."