It's not just the kissing he said was responsible.
He later told the US Anti-Doping Agency (Usada) he had contaminated the substance from his girlfriend.
Roberts said his girlfriend got pills to treat a sinus infection from a "makeshift" pharmacy while on a trip in India and kept taking them in the U.S. Roberts said he gave her a smooch just before providing his urine sample and that medicine must have tainted it. But because she had trouble swallowing pills, she took the medication by just swallowing the powder kept in the capsules.
"Roberts had dated Ms Salazar for two years and surely had kissed her before without being charged with a doping violation", the report said.
It has been acknowledged that incidents such as Roberts's case are rare. He did remember, however, that the two kissed a lot.More news: Rodgers takes lead at John Deere Classic
"They kissed and "chilled out".
Roberts, who had been provisionally suspended, has since competed in the 400m at last month's USA track and field championships, in which he qualified for August's World Championships in London by finishing second in 44.22 seconds, behind Fred Kerley.
According to the report, Salizar met up with Roberts when she was back in the country on the same day he was visited for out-of-competition testing.
Roberts testified he did not know that kissing his girlfriend would lead to a positive drug test.
French tennis player Richard Gasquet also successfully argued that a positive test for cocaine had been due to kissing in 2009, which saw him cleared.