According to US prosecutor Lynn Jordheim, Yao was detained for carrying unidentified biological materials in vials wrapped in aluminium foil inside a glove and packaged in a plastic bag, along with electrical wires, in the trunk of his car.
Yao said in an affidavit he stole the vials, described as research vectors, from the Winnipeg lab on his last day of work there on January 21.
He told US border guards he was taking them to his new job with the National Institutes of Health at the Biodefense Research Laboratory in Bethesda, Maryland.
US authorities feared their contents could pose a terrorist threat. But tests later showed "they are not hazardous," said Jordheim.