(CNN) Donald Trump kicked off his primary campaign with an infamous attack on the Mexican government -- one he was privately searching for evidence to sustain weeks after he made it.

"They're sending people that have lots of problems (across the border)," Trump said at his June 2015 announcement in New York. "They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people."

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It was a remarkable charge, presented without any proof. In his remarks that day, Trump added that he speaks "to border guards and they tell us what we're getting." But even as his young campaign took flight in the weeks that followed, Trump was unsure and seeking new information -- in any form -- to back his initial claim.

During a visit to Laredo, Texas, that July, he found himself in an SUV, speeding toward the border for a photo opp with the city's mayor, Pete Saenz.

"(Trump) asked me whether I knew whether or not Mexico had a policy, direct or indirect, of sending bad guys over here," Saenz told CNN last May , almost a year after the exchange. He recalled telling Trump that he was unaware of anything like it.

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