It looks like it was Elmo's second performer, Kevin Clash
In November 2012, 23-year-old Sheldon Stephens alleged that he had been in a sexual relationship with Clash that began when Stephens was 16, which would be a felony under New York law that declares any sexual relationship with individuals under 17 years of age illegal. Sesame Workshop had initially been presented with the allegation in June, and its investigation found the allegation to be unsubstantiated. Clash acknowledged that he had been in a relationship with the accuser; however, he said the relationship was between two consenting adults. Stephens later recanted his accusation, but two weeks later, another accuser, Cecil Singleton, accused Clash of sexually abusing him when he was 15 years old, and lawsuits were filed by attorney Jeffrey Herman against Clash.