Ethan Sawyer was Temperance Brennan's grad school friend and the murder victim in The Past in the Present. Bones was unofficially consulting with Ethan on Christopher Pelant's case since she knew he was more intelligent than Pelant and dangerous to his plans. He specialized in artificial intelligence and designed mathematical constructs for human behavior.
He was sentenced to a mental institution following his diagnosis with extreme schizophrenia; one 'symptom' included the belief that Brennan's daughter was a demon that was a 'threat' to her mother. Despite the threats to her daughter, Brennan was saddened by Ethan's descent into madness.
His body was found drugged and eaten alive by wolves at the Hamilton National Wildlife Refuge, with Pelant staging the crime and leaving faked digital evidence to suggest that Brennan killed him due to his threats to Christine.
However before he died, Ethan leaves a clue to Brennan and the Jeffersonian within his room at the institution, written in his own saliva as an unidentifiable code in the shape of a triangle. Hodgins and Cam used a black light to find the triangle. Angela is eventually able to decipher the code after Sweets identified each side of the triangle as representations of Pelant's personality. The code is used to prove that Pelant planted Brennan into the video and prove her innocence in his murder.