"My two political heroes were MLK and Bobby Kennedy.
My senior semester, they were both shot and killed," Biden said.
"Imagine if, God forbid, Barack Obama had been assassinated after becoming the de facto nominee.
What would have happened in America?" He then misstated the number of victims from the May 4, 1970 shootings at Kent State University.
"You had over 40 kids shot," Biden said, speaking at a town hall at Dartmouth College.
On May 4, 1970, Ohio National Guard troops shot dead four unarmed people and wounded nine others during a campus protest against the Vietnam War.
Earlier this month, Biden made more apparent misstatements.
During a gun control event in Iowa, he said he met with Parkland shooting survivors when he was "vice president," although he was not at the time.
He had been out of office for more than a year before the shooting.
Before that, during a Des Moines speech about opportunity in education last weekend, Biden said, "We have this notion that somehow if you're poor you cannot do it.
Poor kids are just as bright and just as talented as white kids." Apparently realizing he'd made a mistake, Biden quickly added, "wealthy kids, black kids, Asian kids."