|Affiliation||NYPD's Internal Affairs Bureau|
Cassidy was the youngest and most inexperienced member of the precinct. He was partnered with the most experienced member of the team, John Munch. Cassidy makes a real effort to learn from the other members of the precinct, but he also creates friction between him and his colleagues. In the investigation into the death of two young models Olivia Benson suggests to Munch and Cassidy that they should try a tactic called the prisoners dilemma, in which you get each of the suspects to think that the other confessed. Cassidy gets really excited about this tactic and expresses his love for the job. This earned him a few surprised glares from his co-workers. (SVU:...Or Just Look Like One)
While far from an intellectual, Cassidy is a genuinely talented and driven police officer. He has a genuine desire to put rapists and child molesters in prison, but lacks the professional detachment necessary to deal with particularly grisly sex crimes or remain objective toward victims and perpetrators of sexual assault. Captain Cragen realizes that Cassidy is unable to handle emotionally the stress of investigating sex crimes, particularly those against children. Shortly thereafter, Cragen helps Cassidy transfer to the NYPD's Narcotics Division. (SVU:Disrobed)
Cassidy's relative lack of sophistication causes several problems for him. His co-workers tend to make fun of him, and don't always take him seriously. During the investigation into the death of Victor Spicer, Captain Donald Cragen decides that Cassidy can investigate another crime on his own. In this case it was about a man who molested a dead woman. (SVU:Payback) As the only detective on the case, he has to appear in court to testify against the offender. ADA Abbie Carmichael questions him about the events that lead to the offense. Cassidy is extremely nervous during his time in the witness stand. Defense attorney Hawkins takes advantage of Cassidy's nervousness and lack of sophistication. When Hawkins asks him about the technical term for fondling a stranger, Cassidy comes up with the answer "fromage". The answer was supposed to be frottage. (SVU:A Single Life)
Relationship with Olivia BensonEdit
During his time in the Special Victims Unit he started a brief relationship with Detective Benson.The two had a drunken one night stand and Brian was left wanting to start a relationship with Olivia. Olivia feels that she has broken her personal rule of not getting involved with your co-workers. When he starts to come close to her, she decides to end the relationship. This causes a lot of friction between the two of them during the cases they investigate. When Benson comes up with a theory for a crime, he is the one to make objections against it. While they investigate the rape of Harper Anderson, Cassidy is convinced that she's lying. Although it's clear to the other detectives that she's indeed telling the truth. (SVU:Closure)
More recently, in season 13, Cassidy reappeared in the final episode.It is revealed that he had been working undercover for a while and, during an investigation by Benson and Amaro, Benson and Cassidy met again. After Cassidy gets shot during the investigation he and Benson talk and share a kiss. In Presumed Guilty, Benson reveals that she's going on a trip to The Bahamas with "a friend."
When Detectives Munch and Amaro go to Cassidy's apartment in "Undercover Blue" to inform him he's been accused of rape, they find Olivia in a night shirt. It's revealed that Brian and Olivia have rekindled their relationship after a thirteen year gap. The episode ends with Olivia and Brian going to catch a drink. It's clear Brian has doubts of Olivia's trust. However, they're still together in the season 14 finale, "Her Negotiation." In Season 15, Cassidy and Benson are still romantically involved and move in together. They later break-up in the Season 15 episode "Downloaded Child" and the break-up is amicable for Benson and Cassidy.
- Cassidy had the longest gap between appearances, his last appearance in Season 1 and his reappearance in Season 13's finale.
- He is one of the only two actors from Season 1 to be in SVU today, although Olivia still works in SVU and he currently works in IAB.