Whiteout

In 1957 a Russian cargo plane is flying above Antarctica. In the cargo hold, three Russians sit with a padlocked box. The co-pilot leaves his seat and goes into the cargo hold, then begins to shoot the other men, who return fire. The chaos caused by the gunfight leads to a crash which kills all aboard.
In modern times, newcomers arrive at the United States' AmundsenâScott South Pole Station in Antarctica, while others who are scheduled to leave are preparing to do so early because of a storm. They must depart before the onset of winter or remain for six months. Deputy U.S. Marshal Carrie Stetko (Kate Beckinsale) has been working in Antarctica for two years, since a betrayal by her partner in Miami that killed him and nearly killed her. She plans to retire after returning to the United States in two days.
Stetko, her friend Doc (Tom Skerritt), and pilot Delfy (Columbus Short) fly to the remote Haworth Mesa to retrieve a discovered body. The dead man is Anton Weiss (Marc James Beauchamp), one of a group of three scientists looking for meteorites. An autopsy finds evidence of murder by axe. A murder requires a federal investigation; Stetko considers sending the body to McMurdo Station to avoid spending another winter in Antarctica, but decides to continue the investigation. When Stetko goes to speak to one of the others at Vostok Station, she finds him dying from a neck wound and is herself attacked by a black-clad man with an axe. Stetko injures her hands in escaping, losing the wet skin of her fingers on the metal handle of a door. Later, she finds Robert Pryce (Gabriel Macht), a United Nations security agent, examining the body of the second scientist. They conclude that the third, who is missing, must be the killer and set out to explore the groupâs most recent search site. There, Stetko falls through the ice to find the old Russian cargo plane. Pryce and Delfy join her to investigate, and they realize that the locked box had been opened and six cylinders removed. Pryce reveals that it is possible that nuclear fuel of interest to arms traffickers may be in the cylinders.
After nearly being trapped by a cave-in at the plane, Stetko must have her badly frostbitten fingers amputated by Doc. She then finds the missing scientist hiding in her office. He tells her that he and his two companions found the plane and took the canisters, but the killer has them now. Before Stetko can protect him he is killed, but Carrie captures his killer, who is revealed to be Australian biologist Russell Haden (Alex O'Loughlin). The base commander orders everyone to evacuate because of the murders. With Haden locked in the brig and the winter storm near, Stetko and Pryce search for the canisters.
Stetko checks the last departing plane's cargo manifest and learns that the bodies of the dead scientists were not aboard. She searches their body bags and notices that the stitching on Weiss's old wound matches the distinctive pattern on her amputated fingers. Stetko explores the body and finds several bags of large, uncut diamonds. Doc confesses that he was part of a diamond smuggling ring with the others before Haden killed the rest. He had hoped that the diamonds would make him wealthy outside Antarctica. When Doc tells Stetko he wants to see the aurora australis one last time, she allows him to walk outside to his death.
Six months later, Stetko, Pryce, and Delfy have wintered at the facility. She transmits an email to her superior, rescinding her previous resignation and asking for a warmer location for her assignment.

Question: Who confesses to being part of a diamond smuggling ring?
Answer: Doc