|First appearance||"The Routine" (episode 1.01)|
|Last appearance||"Gray Matter" (episode 4.05)|
|Reason/Cause||Relocates to England with her daughter.|
|Relatives|| Didi Wittlesey (Daughter)|
Unnamed Mother (Deceased)
|Episode Count||23 Episodes|
|Portrayed by||Edie Falco|
Oz's first female correctional officer is a divorcee and single mother, who has suffered spousal abuse, poverty and substance abuse; through all of that she gained a pretty good understanding of criminal life. She is a CO in the Oswald Maximum Security Facility, but she only works there because she can't find work anywhere else.
Her only drive is taking care of her mother, who has cancer, and her young daughter, whom she has to raise all by herself. She works double shifts, sometimes sleeping in the prison, just to make ends meet. Wittlesey is the only primary character who, although she was on for three seasons, was never killed off. She is one of the few characters to have a happy ending to their storyline.
Wittlesey is the supervisor of the guards in Emerald City, Unit Manager Tim McManus' experimental cell block. She helps to keep prisoners' records and to stop any conflicts between inmates. Eventually, she and McManus fall in love and even have sex inside an empty cell. However, when the two receive flak from their fellow staff members over their relationship, she breaks it off with him.
Eventually, Wittlesey gets some bad news — Oz had made a contract with the Department of Corrections that, as a condition, will no longer allow officers to work overtime. More trouble arises for her when Scott Ross enters Oz. He was a biker on the outside; he and her ex-husband used to be in the same biker gang. He is obsessed with Wittlesey, and on the outside he tried many times to have sex with her behind her husband's back. Ross decides to "help her out" with her situation at home; he proposes that she smuggle cigarettes for him and he will give her extra cash. She agrees reluctantly, but when McManus finds out, he tells her to stop. He doesn't fire her, knowing she's only trying to make money for her family. When Ross gets wind of this, he threatens to tell Warden Leo Glynn and take from Wittlesey everything she has worked for.
Wittlesey gets caught in a riot in Emerald City. She is taken hostage, but eventually the SORT team breaks in and ends the riot. Ross shoots McManus (who volunteered to be captive in return for letting two critically injured officers out for treatment). Wittlesey later takes the gun and kills Ross, shooting him in the head, heart, and genitalia.
As Alvah Case investigates the riot, he notices that Ross was shot execution style. Meanwhile, while patrolling Unit B, Vernon Schillinger, leader of the Aryan Brotherhood, tells Wittlesey that he saw her kill Ross and that he will make sure she is exposed. When Case confronts Wittlesey, she admits to killing Ross. Glynn convinces Case that Wittlesey is the best guard he's ever had, that she is struggling to make enough money, and that punishing her for taking Ross' life is not worth ruining hers. Feeling sorry for Wittlesey, Case rules that Ross was killed by bullets from the SORT team members.
Schillinger proposes to Wittlesey that if she helps him kill Tobias Beecher, he will pay her handsomely and keep her secret. She turns the tables against him, however, and sets him up to be charged with conspiracy to commit murder. To get back at her, Schillinger tells McManus the truth about Ross' death. Wittlesey denies it to McManus. Eventually, Wittlesey decides to move back to Emerald City, where she shows an unrequited interest in McManus. He now suspects her of killing Ross, and reopens the investigation. She admits to him that she did do it, but only because Ross shot him first.
Schillinger approached Muslim leader Kareem Said, who was handling cases for various prisoners, and asked him to represent him on the conspiracy to commit murder charge. In investigating the case, Said interrogated McManus and Wittlesey about the murder, and both of them lied. Eventually, the lack of proof buried the truth once more. However, McManus was ridden with guilt for lying, and decided to transfer Wittlesey out of Emerald City and into Unit B.
Wittlesey continues to work in Unit B, and finds another female correctional officer working with her, Officer Claire Howell. Tension soon develops between them, once Howell takes an interest in McManus.
Soon afterward, Wittlesey learns that her mother has died. McManus comforts her, which stirs up tension in his relationship with Howell. Eventually, Howell sues him for sexual harassment, worsening the tension between the two women. Wittlesey takes McManus' side, and the two grow close again throughout the ordeal. In the end, McManus asks Wittlesey to renew their relationship.
When the entire prison is put into lock down amid serious racial tension, Wittlesey fears another riot, and decides to take vacation leave. She goes to England with her daughter.
Wittlesey's vacation was supposed to be finished, but she never came back to Oz, much to McManus' disappointment and agitation, since he intended to propose to her upon her return. She phones Sister Pete, and explains that she is engaged to a Royal Guardsman. McManus is crushed, and barely acknowledges her during a strained long-distance phone call. This leads to McManus having a nervous breakdown, and eventually, losing his job.
- Scott Ross: Shot to death during the riot in Em City. (1997)
Warden Leo Glynn - Tim McManus - Sister Peter Marie Reimondo - Gloria Nathan - Father Ray Mukada - Martin Querns - Lenny Burrano - Dr. Tariq Faraj - Diane Wittlesey - Sean Murphy - Claire Howell - Clayton Hughes - Karl Metzger - Andrea Phelan - Dave Brass - Len Lopresti - Eugene Rivera - Adrian Johnson - Travis Smith - Joseph Mineo - Jason Armstrong - Mike Healy - Gordon Wood - Eddie Hunt - Tom Robinson - Rick Heim - Vic D'Agnasti - Anthony Nowakowski - Lawrence Smith - Joseph Howard - Roger Brese - Carol Grace - Suzanne Fitzgerald