Diana Hawthorne (Laila Robins) is the hidden villainess from Law & Order episode 6.12, "Trophy" (airdate January 31, 1996).
Diana is an Assistant District Attorney who worked for Jack McCoy years prior, and also engaged in a romantic relationship with Jack. In 1990, Diana and Jack served as the prosecuting team against Andrew Dillard, a White Supremacist who was charged in the serial killing of five African-American boys.
Two months before the trial, Detective Monfredo gave Diana a statement he took from a woman named Laverne Chalmers, which implicated an African-American man in killing Jaleel Franklin, the third of the five victims. Diana destroyed the statement and later approached a writing expert, examining the notes left near the bodies to go over his testimony. When he said he couldn't be sure, Diana convinced him to lie on the stand by claiming that Jack had other evidence that was excluded, and she later prevented the expert from speaking to Jack; often making false excuses for his absences. As a result of her villainous cover-up, Dillard was convicted and Diana left the DA's office a year later to set up her own practice.
Also as a result of Diana's actions, two more African-American boys were murdered in the same fashion in the episode's events, and the killer was finally revealed as Simon Brooks, an African-American security guard. Following this, Jack was on the receiving end of a multi-million dollar lawsuit from Dillard, with Diana named in the suit. After ADA Claire Kincaid discovers Diana's role in Dillard's confiction, she met Diana at her office and asked about the case. In response, the evil Diana denied hiding the statement and attempted to implicate Jack as the culprit, using his past strategies as an excuse. She even blamed Jack to his face when he confronted her, stating that he has bent the law numerous times to get convictions.
Detectives Curtis and Briscoe later arrested Diana for two counts of criminal facilitation in the second degree regarding Brooks' two recent victims. During her trial hearing, Diana continued scapegoating Jack, as his promotion was mentioned as a potential motive for Jack. However, Claire managed to get Diana to admit to her role and also admit that Jack's promotion was her own motive, while also admitting that Jack never asked her to do what she did. At episode's end, it was revealed that Diana accepted a plea for solicitation in the fourth degree, and she was sentenced to six months in jail, while losing her license to practice law.