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Everything to Know About Detective Frank Cosgrove on Law & Order

Manhattan is a safer place with this ruthless Law & Order investigator on the case.

By Jessica White

In 22 seasons and counting, Law & Order has seen some talented detectives make their way to Manhattan's 27th Precinct. Detective Frank Cosgrove (Jeffrey Donovan) is one of the most dedicated investigators the squad has ever seen and one of the revamped series' fan favorites. 

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Cosgrove is fearless on the frontlines, with a preternatural ability to sniff out trouble and find the culprit, making him the key to success in closing dozens of criminal cases. And, what he might lack in tact, he makes up for in dedication.

RELATED: Everything to Know About Law & Order's Jeffrey Donovan

Read more about Cosgrove's Law & Order tenure below.

Who is Detective Frank Cosgrove on Law & Order?

Cosgrove is a passionate investigator who made his way to Manhattan's Homicide Squad in Season 21, initially partnered with Law & Order legend Detective Kevin Bernard (Anthony Anderson). He replaced Detective Cyprus Lupo (Jeremy Sisto) after Season 20.

In Law & Order Season 22, Cosgrove could be found surveying crime scenes with his new partner, Detective Jalen Shaw (Mehcad Brooks). When he isn't arresting perps with Shaw, he can be found noodling over cases with ADAs Nolan Price (Hugh Dancy) and Samantha Maroun (Odelya Halevi) as well as the office's tenacious leader, DA Jack McCoy (Sam Waterston).

RELATED: Every Law & Order Detective Across All Seasons

Cosgrove's first impression wasn't the shiniest: His stoic demeanor and occasionally-dated thinking landed him in several tiffs with Bernard. These conflicts came to bear on his new match-up with Shaw, but the two slowly but surely developed a bond as partners. 

Detective Frank Cosgrove (Jeffrey Donovan) appears in Season 22 Episode 22 of Law & Order

Frank Cosgrove and Jalen Shaw's Partnership

Det Frank Cosgrove and Det. Shaw on Law and Order

Cosgrove and Shaw's evolving relationship is one of the most powerful arcs within the new Law & Order as the two incredibly different men combine brains on grueling investigations. The pair met in the Season 22 finale ("Gimme Shelter") after a murder forced them together, initially butting heads due to their drastically different backgrounds.

RELATED: What We Know About Detective Jalen Shaw on Law & Order 

Cosgrove and Shaw balance each other in several ways and never fear correcting each other when their efforts go awry. They primarily handle murder cases, but their investigations often drift into other realms of the criminal world, forcing the dynamic duo to always stay on their toes.

Frank Cosgrove's Mentor, Det. Jerry Ryan

Detective Frank Cosgrove (Jeffrey Donovan) appears in Season 22 Episode 22 of Law & Order

Every hero has his idols and, in Season 22, Episode 4 ("Benefit of the Doubt"), Cosgrove reconnected with his mentor, Detective Jerry Ryan (John Bedford Lloyd), after a young novelist was brutally murdered. Ryan initially seemed paramount to the investigation's success after he teamed up with Shaw and Cosgrove to investigate a potential lead, but then Cosgrove noticed Ryan's unethical police practices.

From planting evidence to misleading witnesses, Cosgrove's mentor fell from his grace as their case became compromised due to his unethical tactics. Their arrest was successful but led Cosgrove to take a step away from his friendship with Ryan and grow even closer to Shaw, a shining example of playing it by the book.

Frank Cosgrove's Family

Lily Cosgrove (Alayna Hester), Julia Cosgrove (Anna Rizzo), and Detective Frank Cosgrove (Jeffrey Donovan) appear in Season 22 Episode 20 of Law & Order

Cosgrove's family life has been the subject of some action on Law & Order, notably his connection with his daughter Lily (Alayna Hester).

In Season 22, Episode 20 ("Class Retreat"), Cosgrove was shocked to find a connection between an adult murder victim named Jerome to his daughter, after she revealed she was school friends with the victim's daughter

Lily explained that, while on a class retreat, Jerome's daughter confessed that her father was abusive and had threatened to kill her. After one of Lily's friends confessed to the murder, Lily was placed on the stand to testify. But when the defense questioned her integrity as a witness, Cosgrove's protective nature stole the show  and he adamantly defended his daughter, despite it putting his own courtroom conduct in question.

Frank Cosgrove on Law & Order: SVU and Organized Crime

Chris Meloni, Mariska Hargitay, and Jeffrey Donovan walking together

Cosgrove is an incredibly valuable detective, so it's only natural that his time on the force has led him to brush shoulders with Law & Order: Special Victims Unit's Olivia Benson (Mariska Hargitay) and Organized Crime's  Elliot Stabler (Christopher Meloni). In the three-part Law & Order crossover event, Cosgrove, Stabler, and Benson found themselves working on the same case in Law & Order Season 22's premiere ("Gimme Shelter").

While enjoying lunch with Lily at a cafe, Cosgrove noticed a young, injured woman fleeing from something or someone and subsequently being hit by a car. As Cosgrove rushed to help, a masked man shot her and fled. After reporting the incident at the precinct, Cosgrove met his new partner, Shaw, who made quick work of getting details on the case.

The young woman was revealed to be a sex worker within a sprawling trafficking ring, leading McCoy to give Benson and Stabler a call to get the SVU and OCCB involved. The 27th Precinct was able to solve the case with Benson and Stabler's help, but it was a white-knuckling race to the finish line. Stabler was just seconds shy of shooting the sex trafficking ringleader, but Cosgrove helped him bring the villain in instead, a sign of his growing maturity as a law enforcement officer.