"I have to show her that I can take everything that she has. Then she's going to remember me."
Not much is revealed about Diane, other than she was raised, and possibly born, in Atlanta, Georgia. She was orphaned at the age of eight when her parents, Charles and Elizabeth, committed a double suicide for unspecified reasons. In her adulthood, Diane became a research assistant at Mendel University while Reid's love interest, Maeve Donovan, was working there; she would go on to stalk her. She applied and was rejected for a Ph.D. after submitting a doctoral thesis about spontaneous cellular death in suicide patients, due to said thesis being biased as it contained references to her own parents. Shortly after Maeve left the university, Diane left as well and pursued an unspecified career at a local junior college.
"That's it, isn't it? I-I-I just- I have to let him see that I'm on your level."
Prior to the episode, Diane had shown up at Maeve's loft outside of Washington, D.C. and, taking Maeve by surprise, abducted her. In the beginning of the episode, Diane, going under the alias of Diane Huntington, is living in the residence of Robert "Bobby" Putnam, Maeve's ex-fiancé and her current boyfriend. When the BAU arrive to interrogate Bobby, Diane leaves the room, addressing Reid as "Doctor" and asking him what is going on. Unbeknownst to viewers at the time, Diane was not the one who called Reid on a payphone from Maeve's house, who was identified as "Adam Worth" and uttered the single word, "Zugzwang". When Garcia and JJ discover that the medium used to obliterate Maeve's face in a photograph is black eyeliner, the team realizes that the unsub is a woman, and Reid, recalling his earlier conversation with Diane and the lack of forced entry at Maeve's residence, makes the connection that she is the stalker. Meanwhile, at the apartment she shares with Bobby, Diane has poured Bobby a glass of wine and dressed herself in clothes she took from Maeve's closet. When Bobby notices the difference in her appearance, Diane becomes increasingly angry. As Bobby falters to understand, she makes a retort and then grabs the wine bottle, smashing it against his head twice and knocking him out.
Later, Diane is seen in a dark room, questioning and threatening Bobby and Maeve at gunpoint. The two victims are bound to chairs with zip-ties. Diane rants about how she did not understand what was so special about Maeve until she saw her bond with Reid. She then discloses that she followed Bobby on the night that he followed Maeve to the restaurant. Claiming she "wants what they [Maeve and Reid] have", she puts a gun to Bobby's head and coerces him into getting Maeve to reveal things about Reid. After Maeve gives her several pieces of information, Diane realizes that she must prove that she is equal to Reid to win him over. Deciding that Bobby is "superfluous", she shoots him in the head, killing him. She then leads Maeve to remember who she is by taking her up on the roof and telling her about pre-death cell decay. The two discuss Diane's thesis, and Maeve tells her that her thesis was rejected because the sample was biased. However, Diane affirms that she is a genius, and when Maeve says "maybe", she forces her on the ledge. Maeve then says Diane should kill her herself, because she will not jump as she aims to see Reid arrest Diane. Later, via webcam, Reid writes out the words "Me for her", and Diane sends him a message through Maeve, which reads, "I left you a present; if you want to find it, it's as easy as pie." Discerning that the "pie" was actually "pi", a pun to make him view Diane as brilliant, Reid and the team discover Diane's location, a loft bordering Maeve's that is registered in Maeve's parents' names.
The BAU quickly arrive at the loft and locate a package for Reid, containing a blindfold. Reid is instructed by Diane to enter by himself, without his gun and bulletproof vest. Directing him at gunpoint, Diane forces him to put on the blindfold and guides him into the loft. In an effort to save himself and Maeve, Reid tells Diane that he has read her thesis and is impressed. He then praises her, even telling her that he loves her and claiming to have arranged for her freedom. Diane removes his blindfold and makes him repeat it in front of Maeve. Looking sadly at Maeve, he says, "I don't love you. Sorry." Diane tries to kill Maeve, but Reid stops her. She then proceeds to kiss Reid and, noting his lack of passion, she realizes he is lying, and during the resultant struggle with the gun, Diane shoots the ceiling, prompting the rest of the team to come on scene. Whilst wrestling the gun out of Reid's hands, Diane shoots him in the arm, subduing him for long enough to take Maeve hostage. As Reid pleads for Maeve's life, Diane gets him to admit that he would die for Maeve, to which Maeve mentions Thomas Merton, a writer Reid and herself bonded over. However, Maeve makes a mistake by mentioning this, as Diane apparently sees this as means of gloating. To this, Diane replies, "No." She then shoots herself, the bullet transecting her skull and hitting Maeve as well, killing both.
Diane stalked Maeve and Bobby for ten months before abducting them. When she did, she blitz-attacked them in their apartments in order to subdue them before taking them over to a secondary location. Diane specifically targeted Maeve, the person she thought did her wrong by rejecting her thesis to be published for a PhD, and, convinced that she was a genius, wanted to take everything from the person she thought took everything from her. At a building in a secondary location, she bound her victims to chairs and interrogated them, later goading Maeve to jump off a roof because of her suicidal ideation surrounding her parents' death. Diane then killed both Bobby and Maeve (the latter during a murder-suicide) with gunshots to the head using a .45-caliber handgun.
"She finally saw me. Just as you see me now!"
No official profile on Diane was made by the BAU. However, the team seemed to agree that she best fit the model of a possessive celebrity stalker, with Reid comparing her to Mark David Chapman. Diane felt unappreciated and ignored, and when Maeve rejected her thesis, she became obsessed with possessing everything Maeve had. She also displayed severe narcissistic and psychopathic traits, as well as suicidal ideation.
- March 2012-January 2013:
- Maeve Donovan (stalked; later bashed her head, abducted, tied to a chair, threatened to throw off a roof, and eventually shot in the head on January 16)
- Bobby Putnam (her fiancé; previously stalked; later knocked out by bashing his head twice with a wine bottle, then abducted, tied to a chair, and shot in the head on January 16)
- January 16, 2013: Spencer Reid (attempted, but survived; was non-fatally shot in the arm)
- Diane bears similarities to Maggie Lowe, a stalker who appeared in Season One. Both stalked love interests of Reid's, killed anyone somehow connected to their targets by shooting them, and directly attacked their targets (though Lila Archer survived her attack while Maeve didn't).
- Diane currently holds the most mentions and references for a single one-time female unsub, with a total of fourteen.
- Season Eight
- Season Nine
- Season Ten
- "A Thousand Suns" (mentioned)
- Season Eleven
- "Entropy" (indirectly referenced)
- Season Twelve
- "Red Light" (mentioned)
- ↑ The term zugzwang in chess is a German word for "compulsion to move", which refers to when one player is at a disadvantage due to having to move a piece even though any move will give the other player an advantage. It has also been adapted for usage in a situation in which someone is forced to make a decision, especially an uncomfortable one.