Tom Matthews

Tom Matthews is a high-ranking Miami Metro PD police official who serves as its deputy chief. Previously, he served as commanding officer of Miami Metro PD Homicide Division and the immediate superior of Lieutenant María LaGuerta. Before this, he was a lieutenant himself, serving as superior of, and best friend of, Harry Morgan. When Harry committed suicide, apparently having burned out from witnessing too many failures in the justice system, Matthews used his influence to bury any indication of suicide, and fulfilled a promise he made to Harry to look after Dexter and Debra; which is what he has done to this day.
Matthews is portrayed as having flaws: nominal racism and serious political ambition, neither of which are ever shown in the novel series.
While having originally promoted LaGuerta, he frequently clashed with her, trying to keep her focused on hunting the Ice Truck Killer correctly. Later, however, he fails to take his own advice, as, when Neil Perry was mistakenly arrested, and Matthews received all the praise, he went so far as to try to bury any evidence to the contrary. Seeing the investigation was being jeopardized, LaGuerta revealed that several mistakes during the Ice Truck Killer case had been made, landing Matthews in a world of trouble. Due to the fact he was friends with both the police commissioner and the review board, Matthews escaped punishment and, having been personally embarrassed and wanting vengeance, Matthews laid all the blame on LaGuerta, and so gained approval to install Esme Pascal as the new lieutenant; to supervise her. This proved temporary, however, having later seen Esme break down and regained his confidence in LaGuerta's abilities, Matthews restored her to her previous position.
Matthews' latest political effort, applying for the position of deputy chief, succeeded after Matthews used the fame of successfully ending the Bay Harbor Butcher case to propel himself to that position. Matthews did not appear in Season 3, but re-appeared in Season 4, having succeeded in being promoted to deputy chief, personally invested in the investigation surrounding Frank Lundy's death, and Debra's shooting. After LaGuerta and Batista reveal their relationship, he initially wants to transfer Batista out of Homicide to avoid complications during a trial. Eventually, LaGuerta and Angel both agree to end their relationship to continue working in Homicide; and while accepting this, Matthews warns them that there will be serious consequences if their relationship continues. After revealing a video of LaGuerta and Batista kissing, LaGuerta calls Tom out, asking if it was because of her gender or race that he seems to have a grudge against her. Matthews simply replies he has a grudge against her because of her arrogance. In order to circumvent a reprimand from higher up, and also as a result of their deepening feelings for one another, LaGuerta and Batista secretly get married with Dexter as witness.
In the sixth season premiere, Matthews oddly has promoted LaGuerta to captain, which many characters note as unusual. After the ceremony, however, it is shown that LaGuerta had found a "little black book" of a brothel with Matthews' name in it, trading the evidence for her promotion. Accordingly, her promotion left the lieutenant position open, which LaGuerta attempted to secure for Batista. However, Matthews declares Debra a more suitable candidate, being young and famous after a shootout at a restaurant in which Debra and Quinn were involved was recorded and posted online. LaGuerta and Batista both believe that he did this in vengeance, though little was proven. His prostitute-hiring tendencies leads to a call girl dead from a heroin overdose, which while not his fault, led to LaGuerta attempting to cover up the no-fault crime scene claiming the low clearance rate as unacceptable. However, Debra continues to search after a visit from the call girl's parents, leading to her discovery of Matthews' involvement. LaGuerta used the information on Tom and betrayed him and had him forcibly retired by the board when she told them. Tom however, believed it to be Debra who sold him out but she stated she never would do that and Debra would confront LaGuerta for doing such a low tactic, knowing full well she did it for her own personal gain. As such, LaGuerta will now take over Tom's position possibly as Deputy Chief.
After much absence, Tom is finally brought back during LaGuerta's suspicion that Dexter is the BHB. He is seen on his boat drinking scotch greeting LaGuerta as she confides her suspicion that the BHB is alive and well. Tom doesn't believe her, stating the evidence was all against Doakes, but seems to show surprise after hearing a blood slide was found at Travis Marshall's church site. Though reluctant at first, Tom decides to help after discovering LaGuerta was the one who sold him out to the board and shows his anger despite LaGuerta stating he started it. He intends to help for his own reason for his 40-year pension despite LaGuerta's displeasure at the prospect.
As they dig into the case, they revisit the cabin Doakes died in and discover that Santos Jimenez had rented the cabin, prompting Tom to realize who he is and reveal to LaGuerta that Jimenez is responsible for Dexter's mother's death and changing Brian, Dexter's brother, into becoming the ITK. This causes LaGuerta to, after hearing Jimenez's disappearance and Dexter's background, immediately start to believe Dexter set Doakes up and he is the true BHB. Tom however, refuses to believe her and prevents LaGuerta from questioning him, stating he'll do it having known Dexter since he was a boy.
As Tom talks personally to Dexter, he confides how LaGuerta believes he is the butcher (though Dexter is able to see that Tom also believes it in some way.) Dexter then tells him about a boat Doakes once had to lead him off the case which has Tom believe him. He tells LaGuerta about this and she doesn't believe him stating she would have known if Doakes had a boat. They find a tackle box from the old cabin and find a key to a marina and, believing it to be Doakes's old boat spot, search the area and find several sheets of plastic, knives and one with degraded blood on it with Doakes's fingerprints on it. This causes Tom to immediately believe Dexter, but LaGuerta still believes otherwise stating Dexter could have planted (which is actually true) it despite Tom's refusal and that Maria should move on. She says she'll keep her word and give Tom his pension and later is visited by Dexter where the two make amends for each other's suspicions.

Vince Masuka

Vincent Masuka is the Miami Metro Police lead forensics investigator and works alongside Dexter in the lab and in crime scenes.^[2] He often cracks innuendo to the rest of the team, and harbors decidedly unrequited feelings for Debra. He is portrayed as obsessed with sex, often makes inappropriate comments with implied sexual meaning on the crime scenes ended with characteristic for him laugh. The kinkier the better- he is not shy about propositioning any woman he meets. However, he has been able to tone it down when the situation calls for it, like when Angel was in hospital, as well as calming Debra down when Lundy returned. Detective Joey Quinn even confronted him about it, stating that his comments are why nobody likes to be around him, only for Vince to harshly brush him off. However, he seems to accept Joey's explanation when no one came to see his speech on his newly published work, for which he cleaned up his act and dressed formally, but soon returned to his former self. In the books, Dexter feels a kinship with him as, like him, he hides who he really is. In the novel as well as in the series, he sets up Dexter's Bachelor Party and kidnaps him to get him there (where, in the belief that he had been kidnapped by Ramon Prado, Dexter slugged Vince in the eye just as he opened the car trunk). However, he falls for the female Party Planner and it has been suggested they are still in a relationship. He is also shown to be greatly distraught after seeing Rita kiss another man, leading him to try to tell Dexter. In season 5 it is discovered that he has a giant tattoo of a dragon on his back.
In the novels, he is the closest thing Dexter has to a friend; Dexter senses that they are both pretending to be normal, albeit for completely different reasons. In Dearly Devoted Dexter Vince throws a large bachelor party for Dexter within a few hours of finding out about his engagement, and in Dexter in the Dark takes his role as best man so seriously that he calls in favors to hire Manny Borque, a famous caterer, for Dexter's wedding.

Doakes

James Doakes is a sergeant serving as lead case investigator to Miami Metro PD's Homicide. Doakes had killer impulses which drove him to divorce his wife, confessing that if he had stayed with her any longer, he would have killed her.
Doakes instinctively hates Dexter; and is the only person in Dexter's life who can see through his mask of normalcy, Doakes suspects that Dexter is hiding something and has no reservations about telling him so. Ultimately, Doakes realizes that Dexter is withholding vital information on the Ice Truck Killer case and his frustration drives Doakes to physically attack him, only for Dexter to expertly fight back. Doakes' friend LaGuerta tells him to back off, but Doakes begins following Dexter in secret.
Doakes temporarily ends his stalking when he finds Dexter attending a Narcotics Anonymous meeting, supposedly for heroin addiction. Doakes erroneously believes Dexter's dark secret is that he is a drug addict whose addiction is caused by work-related stress, Doakes tells Dexter that he has seen many policemen led down the same path. Feeling sympathetic towards Dexter, Doakes briefly leaves him alone.
Doakes resumes the hunt, however, when Debra innocently reveals that Dexter does not so much as smoke. On finding Doakes meddling in his past again, Dexter goads him into a seemingly unprovoked fight in front of the entire squad room. Doakes breaks into Dexter's apartment, and stumbles upon Dexter's blood slide collection box, and realizes Dexter's secret—that he is the Bay Harbor Butcher. Ironically, Doakes is by now the prime suspect in the case, thanks to Dexter's manipulation of the evidence.
Doakes attempts to apprehend Dexter himself in the Everglades, but Dexter gets the upper hand and locks him in Jimenez's cabin while deciding what to do. Doakes tries to convince Dexter to turn himself in; however, Lila Tournay finds the cabin and blows it up by igniting propane tanks after finding out that Dexter is the Bay Harbor Butcher. Doakes' incinerated remains are found along with the dismembered body of Jose Garza, and so the case is closed, with the official conclusion being that Doakes was the culprit.

Joey Quinn

Joseph Quinn is a detective who transferred to the Homicide division after being in Narcotics before Season 3. Quinn takes a liking to Debra Morgan, even giving her a C.I. to help with the Oscar Prado case. Quinn's past is unknown and even called into question, as Debra is pressured by Internal Affairs agent Yuki Amado to gather evidence against him. Quinn got the Internal Affairs case dropped, and later confessed to Debra that the real source of the Internal Affairs investigation was from the death of a former partner of his and Yuki's who had a crystal meth addiction. Quinn knew about the partner's addiction but tried to offer private help instead of informing his superiors. He is seen at Dexter's wedding, despite Debra's advice to Dexter against inviting him.
At the beginning of season 4, Quinn is infuriated when Dexter botches a case he worked on. Soon afterwards, Dexter sees Quinn stealing money from a crime scene, and Quinn attempts to buy Dexter's friendship with expensive football tickets, but Dexter gives them away to Masuka. Meanwhile, Quinn starts a relationship with Christine Hill, a seductive reporter who takes advantage of his access to police information. After a confidential police lead appears in one of Hill's articles, Lt. LaGuerta warns Quinn to be wary of any reporter who squeezes him for confidential information over pillow talk. Nonetheless, Quinn tells Hill about numerous police reports (supposedly "off the record"), and she uses this information to expose Frank Lundy's return to Miami. Quinn breaks up with Hill after the article about Lundy, but they soon make up. Though more careful about what he says around her, Quinn still defends Christine when Dexter tells her to leave Debra alone, as Hill claims to have wanted to do a "hero piece" on Debra. All of this leads to Quinn developing a confrontational relationship with Dexter. After Hill, revealed to be Trinity's daughter, shoots herself, he is clearly distraught.
In Season 5, he strongly suspects Rita was really murdered by Dexter and not Trinity, because of subtle differences in MO and because Rita shared a kiss with the neighbor. He also believes that Dexter was the Kyle Butler that was hanging out with Arthur. He tracks down Trinity's son, hoping he can identify Dexter as Kyle, but he is stopped by the FBI and suspended by LaGuerta. Unable to continue, Quinn hires Stan Liddy to investigate Dexter. After a one-night stand with Debra, Quinn repeatedly tries to get her back into bed, eventually succeeding as the two begin to date, until Debra discovers that Quinn was suspended by LaGuerta for investigating Dexter, and not taking vacation days as he had said. Liddy begins to harass Quinn but Quinn does not wish to continue investigating Dexter because of his romantic feelings for his sister, Debra. Stan Liddy was killed by Dexter in self-defense. Quinn is the main suspect because there is blood on his shoe and numerous calls between his phone and Liddy. Dexter makes the blood evidence on Quinn's shoe go away and Quinn is once again a free man. Quinn thanks Dexter, who plays dumb and just says "For what? Just doing my job."
In Season 7, Quinn falls for Nadia, a stripper who works at a club, The Fox Hole, operated by the Ukrainian Koshka mafia. He steals evidence that would have convicted Isaak Sirko in an attempt to win Nadia's freedom from Koshka control. However, after freeing her from her strip club job, Nadia runs away to Las Vegas leaving Quinn brokenhearted. In the season finale he is seen having drinks with Angel Batista's sister.

Angel Batista

Angel Batista is a detective in Miami Metro Police Department's Homicide Division. Batista is basically good-natured, with a dry sense of humor. He is also totally honest, at the request of his father on his deathbed. Angel is also shown wearing a trilby hat almost all the time. After having an affair with another woman, he confesses his actions to his wife; she immediately ends their relationship, although it takes months for the painful separation to conclude.
Angel takes an interest in Lila and eventually ends up sleeping with her. However, Lila takes rohipnol and then files rape charges against Angel. During this period, Dexter admits that if he were "normal", he would want to be a man like Batista. Ultimately, the charges are dropped once Lila moves to Paris.
At the start of season 3, Batista is promoted to sergeant and made the department's new lead case investigator to replace the now-deceased Doakes. However, he risks his career by attempting to sleep with a hooker who turns out to be an undercover cop. After persistent but gentlemanly advances, Angel begins a relationship with the other officer, Barbara Gianna.
By the start of Season 4, it appears that Angel and Barbara have amicably split, and he has a romantic involvement with LaGuerta, although this is kept hidden from those they work with. In "Hello, Dexter Morgan", they secretly get married with Dexter as witness. By season 5 their marriage has become common knowledge throughout the office.
Batista and LaGuerta divorce in between seasons 5 and 6.
In season 7, Batista buys a restaurant, and announces his retirement although in season 8 he still continuous to work for the Miami Metro PD as a Lieutenant.