|“||Mike, I get it. You want to do the noble thing here. But I got news for you: there ain't so such thing as noble.||„|
|~ Murphy accidentally revealing his treachery|
Police Lieutenant Alex "Murph" Murphy is the secondary antagonist of The Commuter.
The ex-partner of Michael MacCauley, Murphy is first seen meeting up with Michael at a bar. Michael laments that he had just lost his job as an insurance agent as Murphy tells him that Sergeant David Hawthorne had been promoted to Captain. Murphy pays for Michael's drinks as he leaves.
On his train ride home, Michael meets a mysterious woman named Joanna. Introducing herself as a psychologist, Joanna asks Michael to imagine a "hypothetical" scenario: someone on the train by the alias "Prynne" doesn't belong and is headed to Cold Spring, $25,000 is hidden in a bathroom and $75,000 will be rewarded if he finds Prynne. Joanna leaves and Michael finds $25,000. When he attempts to leave the train without searching for Prynne, a teenager accosts him and gives him an envelope with his wife's wedding ring, forcing Michael to stay and try and find Prynne.
Michael attempts to ask his friend Walt for help, but when Walt is killed, Michael borrows a man's phone and calls Karen and then Murphy. When Murphy doesn't respond, he convinces the conductor to check the bags of the other passengers. Michael then gets into a fight with a suspicious man and plants a GPS tracker on him. Murphy calls back explains that Prynne is the witness to the murder of city planner Enrique Mendez. Michael then finds the corpse of the man he planted the GPS tracker on and learns that he was an FBI agent (presumably escorting Prynne). He is forced to hide with the corpse to avoid a police inspection and barely manages to get on the train, only to lose most of the $25,000 except for a $100 bill.
Dismantling the air conditioning system, Michael manages to gather all the other passengers in the last car and makes vague conversation about his situation in a game of poker. After a fight with another passenger, Oliver, Michael holds the other passengers at gunpoint with Oliver's gun as he attempt to discern who is Prynne. He finally deduces Prynne as Ernique's cousin Sofia, but the conductor spots him and calls the police. When Michael is unable bring himself to kill Sofia, Joanna sets off a bomb and almost derails the train, the conductor sacrificing his life to disengage the final carriage.
After the rocky landing, Michael orders the other passengers to stay in the car and cover the windows with newspapers, in case other members of the conspiracy attempt to attack them, and wait for the police to arrive. Sofia tells Michael that Ernique was killed by a cop who mentioned something about how there's no such thing as being noble. Just then, the police surround the car. Believing Michael to be a hijacker, they demand he surrender and let the hostages out.
Murphy is sent to negotiate with Michael, who is paranoid of the conspiracy infiltrating the police. Murphy gives himself up as a hostage in exchange for other passengers. As he speaks with Michael, he talks about doing "the noble thing" and Michael realises that he's the cop who killed Ernique Mendez and that Murphy set Michael up. He attacks and threatens Murphy, but Murphy gets him to back off and give him the gun by threatening to tell Joanna to have Michael's family killed. Murphy admits that he set up Michael up, hoping that he would take the bait
Murphy then demands Prynne to give up their identity. Sofia does so, but the other passengers also announce themselves as Prynne. Michael tackles Murphy, who prepares to shoot down the passengers and frame Michael. However, Michael grabs Murphy's "friendly" electronic ID tag and police snipers shoot and kill Murphy.
While acknowledging Murphy's betrayal, Michael deduces that he was just another victim of Joanna's manipulation and arrests her later.
- In the beginning, Murphy mentions that he's 45, divorced and is estranged from his children.
- On the train, Murphy tells Michael that he's "got a family too", implying that his family is also being threatened by the conspiracy.