From Castle Case Files
Deceased mother of Detective Kate Beckett and former wife of Kate's father, Jim Beckett. She worked as a civil rights attorney, championing the rights of people who others have ignored,  and law professor. She frequently worked with an organization called the Justice Initiative and once organized a group of neighbors together in an effort to rid a nearby neighborhood of drug dealers.
She was fond of saying "I told you so" to Kate, to the extent that in Sucker Punch (episode 2.13), Kate refers to the expression as "Mom's favorite words."
Click here for a link to the Murder Board for Johanna Beckett's case.
In January of 1999, when Kate was 19 and in college, roughly ten years before Kate meets Richard Castle, Johanna was stabbed to death in an alley. In A Chill Goes Through Her Veins (episode 1.5), Kate tells Castle that she an her father Jim Beckett had planned on having dinner with Johanna, only her mother never showed at the restaurant. When she and her father arrived home, they found Detective John Raglan waiting for them to break the news. Johanna's money, purse, and jewelry hadn't been taken, so the motive could not have been robbery. Detective Raglan chalked up the murder to random gang violence and moved on to other cases, leaving Kate and her father without closure. Her father became an alcoholic for about 5 years, but later sobered up with Kate's help. Kate changed her entire life's focus and became a cop, seeking to deliver the justice she never got to other victims of crime.
In A Death in the Family (episode 1.10), Castle asks Kate if she ever considered reopening her mother's case. A shocked and hurt Kate responds that if Castle looks into it, their partnership is over. She goes on to tell him that solving her mother's case obsessed her in her early years as a cop (she spent all her free time for her first three years on the force investigating the case) and that, after a year of therapy, she eventually found she had to let it go, otherwise it would destroy her. Castle ignores her warning and enlists the help of Dr. Clark Murray, who discovers a link between Johanna's murder and the death of one of her students and a law clerk. Castle tells Lanie of the connection in Deep in Death (episode 2.1).
In Sucker Punch, Kate tells Castle that every time she crosses the tape at a crime scene she is reminded of the night she and her father were shown her mother's body in the alley. Castle's friend, forensic pathologist Dr. Clark Murray, tells Castle, Beckett, and Beckett's best friend Medical Examiner Lanie Parish, that her mother had been stabbed with a knife specially made and used by military Special Forces. The killer would kill his victims by stabbing them once fatally, then stabbing them multiple times more to disguise the damage done by the first blow. Beckett and Castle eventually identify the man who murdered Johanna, a hitman named Dick Coonan, and he admits to being ordered to kill her, but Beckett is forced to fatally shoot him before he can tell her who ordered the hit. All he says to her is "You'll never touch him."
In Knockdown (episode 3.13), Detective Raglan contacts Beckett, saying he has information about her mother's murder that he wants to share with her before he dies of lymphoma. She brings Castle long for the meet, and Raglan tells her certain people noticed when Coonan's killing ended up in the press and that he did what he was told when it came to sweeping Johanna's murder under the rug. He tells her that 19 years ago he made a bad decision that eventually cost Johanna her life, but before he can say more, he is shot by a sniper and killed. As Castle and Beckett look into her mother's murder, and Detectives Kevin Ryan and Javier Esposito investigate Raglan's, they discover 19 years ago Raglan was involved in a conspiracy to cover up his and two other cops' participation in a kidnapping ring whereby the cops kidnapped, threatened, and ransomed low level mobsters in an effort to control crime. The plan fell apart, however, when Raglan and his associates accidentally murdered an undercover FBI agent, Bob Armen, instead of mobster Joe Pulgatti, their original target. To cover up the crime, Raglan pinned the murder on Pulgatti, who pled guilty and was eventually convicted. Seven years later, Johanna Beckett agrees to reexamine his case, with the help of a court clerk and two volunteers. All four are murdered by Coonan to prevent the kidnapping ring, and those behind it, from being exposed. As a result of both investigations, they cross paths with a shadowy man going by the name Hal Lockwood, who kidnaps and tortures Ryan and Esposito in an effort to find out what they know about Raglan's murder and the conspiracy. They eventually discover Lockwood murdered Raglan, but he refuses to give up his real name or the identity of who hired him to protect the conspiracy. Beckett vows to meet him every week until he decides he wants to come clean.
In Knockout, Lockwood escapes from prison after killing McAllister. As Beckett and her team try to find him and how he escaped, they uncover the fact that Lockwood was sprung to come after Captain Roy Montgomery, Beckett's boss, because he was the man who accidentally shot Bob Armen. When Beckett became a cop, Lockwood made a deal with Montgomery that he would let his family and Beckett live if Montgomery agreed to keep Beckett on a tight leash. However, Ryan and Esposito expose him to Beckett just as she meets Montgomery, who confesses everything to her. He tells her he used their meet as a means of getting Lockwood into the open so he can kill him and end everything. He refuses to tell Beckett who is controlling the conspiracy in a last effort to protect her since he knows she will go head-long after them, but does say that the person behind it all took all the ransom money he, Raglan, and McAllister had collected and "used it to become what he is." Beckett forgives Montgomery, but refuses to let him sacrifice himself for her, and has to be dragged away, kicking and screaming, by Castle. Montgomery kills Lockwood and his associates, but dies in the effort. At Montgomery's funeral, an unseen assassin shoots Beckett in the chest as she gives the eulogy.
Beckett barely survives being shot and upon her return to work, plunges back into trying to solve not only her mother's murder, but the mystery of who shot her. Ryan and Esposito suspect that an unidentified hitman disguised as a cemetery groundskeeper is the shooter, but the man disappears quickly. Castle initially agrees to help Beckett with the case, despite the fact that their new Captain, Victoria Gates, shut down the investigation for lack of new leads. He changes his mind, when, unbeknownst to Beckett, a mysterious man named Smith contacts Castle and tells Castle that, thanks to a stack of files Montgomery sent him before his death, he succeeded in blackmailing the people behind the conspiracy into staying away from Beckett under threat that he will expose the conspiracy and destroy them. In exchange for their leaving Beckett alone, she has to stop investigating Johanna's death and Castle must help keep her away from the case. Castle agrees and convinces Beckett to let it go, but tells her it is to keep her from destroying herself. Also unbeknownst to Beckett, he begins his own investigation into the conspiracy.
In Dial M for Mayor, Castle and Beckett investigate the murder of a woman connected to Castle's friend, New York City Mayor Robert Weldon, who is responsible for keeping him at the precinct despite that fact that Captain Gates wants him gone. As the investigation progresses and it looks like the Mayor is involved, Smith contacts Castle again and gives him advice that helps him solve the case and exonerate the Mayor. One of the Mayor's aides had let slip to the victim, Laura Cambridge, his involvement in a plot by an unknown, powerful person (via Smith's connection, we assume this is the person behind Johanna's murder) to destroy Mayor Weldon, who was contemplating a run for Governor, and his administration. When the aide discovered that Laura was trying to expose the plot, he called his handlers who dispatched a hitman to kill her. Smith also tells Castle that the Mayor needs to be kept in office so Castle can stay in the precinct and keep Beckett from looking into her mother's case. He calls him a "well-placed pawn."
The trail picks up again in Always when Beckett and the team identify Cole Maddox as the same man who shot her and who orchestrated a break-in of Montgomery's house to steal old family photos which will lead him to Smith's identity. As Beckett doggedly pursues the case, Castle reveals his contact with Smith and the deal he made to save her life and begs her to walk away from the investigation. She is furious and he ends their partnership after she refuses to give up, but Beckett forgives him when she barely survives a confrontation with Maddox. Maddox escapes and finds and tortures Smith into revealing where he has hidden the file. In After the Storm, Beckett, Castle, and Esposito find it at the same time as Maddox, but Smith rigged the safe in which the file was hidden to explode once opened, resulting in Maddox's death and the file nearly being destroyed. The team, including Ryan, piece the papers together and discover an old bank account number indicating that the file included copies of money orders that show deposits of the ransom money taken from Montgomery, McAllister, and Raglan. They trace the bank account to a powerful U.S. Senator, but when Smith is killed, they realize not only is Beckett the next target, but they cannot prove the Senator's complicity. Refusing to be afraid anymore, Beckett confronts the Senator, who hides behind all the good he has done in office and reminds her she is powerless against him. She then threatens to go public with her evidence, which he doesn't know is scanty, and ruin his career if he tries to come after her or anyone she cares about. To make her point, she scratches him across his cheek, telling him the scar left behind will be a reminder that he should be afraid of her. He agrees to back off and Beckett is satisfied that she will eventually get justice for her mother.
Kate wears Johanna's wedding ring on a chain around her neck to remind her of the life she lost and her father's watch on her wrist to remind her of the life she saved.