Diana Hawthorne is an attorney who used to work for Jack McCoy in the Manhattan DA's office and was in a relationship with him. It was ultimately revealed that she played a part in falsely convicting an innocent man of serial murder.
Hawthorne first started working for Jack McCoy in 1987 and eventually entered into a romantic relationship with him a year later. In 1990, Hawthorne worked with McCoy in prosecuting a white supremacist named Andrew Dillard, who was accused of killing five African-American boys. Two months before the trial, Detective Monfredo gave Hawthorne a statement he took from a woman named Laverne Chalmers. This statement implicated an African-American man in killing Jaleel Franklin, the third victim, and Diana destroyed it. She 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, she convinced him to lie on the stand by claiming that McCoy had other evidence that was excluded. The writing expert asked to speak to McCoy but Hawthorne made an excuse for why he couldn't. As a result, Dillard was convicted and Hawthorne left the DA's office a year later to set up her own practice.
After two more African-American boys are killed the same way in 1995, the real killer is revealed to be an African-American security guard named Simon Brooks. When Dillard files a lawsuit against McCoy and everyone involved in the case, Hawthorne is named in the lawsuit. ADA Claire Kincaid later uncovers Hawthorne's role in hiding the statement from the defense and visits her in her office. When asked, she denies her involvement in hiding the evidence and says she gave the statement to McCoy. She implies that he was the one who hid the statement and not her, using his past strategies to cast the blame, although Kincaid is doubtful. She tries to use Hawthorne's past relationship with McCoy and says she is biased, while Hawthorne implies Kincaid is too.
When her role in convincing the expert to lie was uncovered as well, McCoy met with Hawthorne outside her office to confront her. Hawthorne fires back with how many times he bent the law to get convictions, while McCoy says Hawthorne broke the law to get a conviction. She continues to say that it was because of McCoy that she did it. Outraged, McCoy has her arrested by Detectives Briscoe and Curtis for two counts of criminal facilitation in the second degree in the deaths of Derrick Walters and Sean Monroe.
In a meeting with a judge, her attorney tries to dismiss the charges, arguing Hawthorne cannot be held responsible for Brooks' killing spree. McCoy argues that the police would have caught Brooks if not for Hawthorne's actions. When the judge denies her motion, she claims McCoy is covering up his own part in falsely convicting Dillard to save his reputation. As a result, the judge allows Hawthorne's defense in. Her trial is held the following year. She listens to McCoy testify for Kincaid, and then watched as her own attorney imply McCoy did it to expedite his promotion.
Hawthorne later takes the stand, where she smears McCoy and says the whole thing was his idea. When Kincaid cross-examines her, she gets Hawthorne to admit McCoy never asked her to do any of those things. She then has Hawthorne realize that she did everything to help McCoy get that promotion. Hawthorne later talks with McCoy to congratulate Kincaid on revealing the truth that even she wasn't aware of. After this, Hawthorne accepts a plea for solicitation in the fourth degree. She is subsequently sentenced to six months in prison and hands over her license to practice law. This eventually opened the floodgates for every defendant she helped convict to file appeals in their cases. (L&O: "Trophy")
She was eventually released from prison and what happened afterwards is unknown, other than the fact that she is later deposed by Independent Counsel William Dell about her history with McCoy. (L&O: "Sideshow")