Who killed Dinah Brand in Red Harvest?

In Chapter 27 of Red Harvest, Reno Starkey confesses to the murder of Dinah Brand.

Accordingly, the story is set in a small town, Personville, which has been overrun by rival groups of gangsters. Donald Willsson, a newspaper publisher, had originally hired The Continental Op, a private detective, to take down the four rival crooks who were running the town. However, Donald is murdered before he gets to meet with The Continental Op.

Determined to discover the identity of Donald's murderer, The Continental Op sets to work. He discovers that Personville is actually under the control of four rival factions, each headed by an unscrupulous leader: Lew Yard, Pete the Finn, Max Whisper Thaler, and Noonan. While Pete the Finn is a bootlegger, Thaler owns a gambling joint, Noonan is the police chief of Personville, and Lew Yard owns a business dealing in stolen goods. All four turn Personville into a killing zone riddled with dead bodies.

Basically, the Continental Op takes advantage of the rivalry between the gangster groups to rid Personville of corruption. He's the quintessential anti-hero, the kind who has no problems resorting to ruthless measures to take down the criminal element in a defenseless town. He befriends Dinah Brand, the femme fatale of the story. Dinah is very much her own woman; she loves men but is even more enthralled with the prospect of monetary gain.

Even without good looks, style, and grace, Dinah knows how to handle men. The Continental Op falls under her spell and comes to appreciate her softness and warmth. Despite his infatuation, The Continental Op is still a hardened detective; he uses Dinah's shady relationship with Whisper Thaler to uncover incriminating information that he can use for his own purposes. Meanwhile, Reno Starkey, a member of Lew Yard's group, plots with Chief Noonan to frame Whisper Thaler for a bank robbery. At this point, all hell breaks loose, and the gangsters go for each other's throats. Afraid for her life, Dinah begs Reno to protect her from Whisper Thaler. However, Reno himself is spooked and kills Dinah Brand instead; in an effort to avoid being incriminated for his actions, Reno conveniently frames The Continental Op for the murder.

With Dinah and a whole host of gangsters dead, the last two holdouts, Whisper and Reno, engage in a deadly standoff. Reno manages to kill Whisper but is badly wounded as a result. Before his death, Reno confesses to The Continental Op that he was the one who killed Dinah. The story ends on an ominous note; even though the rival gangsters have been killed off, readers get the sense that lasting peace in Personville may be an illusion at best.