The Man

The story starts with Andy Fiddler (Eugene Levy) preparing a speech that he is going to give to a dental convention in Detroit. He works for a dental supply company, and lives in Milwaukee, Wisconsin. Meanwhile, in Detroit, an federal armory (weapons room) of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) has been robbed of assault rifles, handguns and ammunition. An ATF agent was killed and Internal Affairs agent Peters (Miguel Ferrer) suspects the dead agent and his partner Agent Derrick Vann (Samuel L. Jackson) were in on the robbery.
After a visit to his informant Booty (Anthony Mackie) (who is later gunned down), Vann,attempting to clear his name, sets up a buy. He is to go to a diner and be reading a copy of the newspaper USA Today to be recognized. Unfortunately, Andy is also in the diner, and he has a copy of USA Today. He is mistaken for Vann. A menacing Englishman called Joey (Luke Goss) sits next to Andy and hands him a paper bag with "his taste" in it then leaves. The bag contains a cell phone and a gun, which Andy pulls out. The waitress of the diner thinks than Andy is there to rob the place and panics. An arriving Vann arrests Andy, before realizing that the gun traffickers mistook Andy for Vann himself. The received cell phone rings and Vann answers the call. The caller is Joey, who wants "Turk" (the pseudonym that Vann used when setting up the buy) to drop $20,000 dollars in a certain trash can. Vann reveals that he has the money, but now needs Andy to deliver it.
The initial attempt to deliver the money to the gun traffickers fails due to the interference of a bystander. Vann gets another cell phone call from Joey, asking him what happened. He tells Joey that there were complications, and Joey agrees to arrange another attempt at delivery. Meanwhile, Andy tries to escape and Vann shoots after him, grazing him with a gunshot to the rear. Andy uses the cell phone to call the local police for help, resulting in the capture of both of them by arriving squad cars. The police releases Vann after learning that he is an ATF agent, but they discover there is an outstanding warrant for Andy. He reportedly only purchased a stolen rug without knowing of its origins, but he is still suspected of criminal activity.
Vann arranges the release of Andy, to use him in his case against the gun traffickers. Vann tries to contact gun dealer Manny Cortez for help with the case, but finds Manny murdered in his own house. Andy attempts to escape again and fails. Vann then receives a phone call from his ex-wife Dara (Rachael Crawford), who reminds him about the upcoming dance recital of their daughter Kate (Tomorrow Baldwin Montgomery). He then receives another phone call from Joey, who now asks for 500,000 dollars for the whole batch of weapons. Vann has Andy pose as a powerful trafficker for a meeting with Joey in a restaurant. Andy improvises by returning the cell phone to Joey and telling him that their next meeting will be on his terms. Andy plans to use the next meeting to set up a trap for Joey. Andy then convinces Vann that he should attend his daughter's recital, and both men attend it.
Andy and Vann eventually arrange a meeting with Joey, but (against Andy's original plan) they have failed to arrange backup from any law enforcement agency. Joey has never met Vann before and asks who he is. Andy claims that Vann is someone who will do anything they tell him. Vann admits this, and claims that he is betraying the service in pursuit of monetary gain. Joey is suitably convinced and agrees to work with him. Following the meeting, Andy and Vann part ways.
Andy stays in Detroit as planned and delivers his speech. He is then captured by agent Peters, who wants to use him against Vann. Peters claims that Vann is corrupt, that he is actually trying to buy the guns for himself, and that Vann himself murdered Booty, Manny Cortez and Vann's own partner. Peters wants Andy to wear a wire and get a confession out of Vann. Meanwhile, back at ATF offices, Vann is suspended, and his boss (Susie Essman) tells him that Andy was setting him up. Andy, now wired, enters Vann's office and says they need to talk. The two men drive to the exchange point to deliver the money. Vann suspects that Andy is wired and asks him about it. Andy admits it.
Vann and Andy enter the barn where the exchange is going to take place. This time Joey is skeptical of their motives and pulls a gun on Vann. The law enforcement agents hear everything through the wire, and soon arrive to arrest Joey. Andy manages to disarm Joey, though Vann still receives a bullet wound in the buttocks. Vann delivers Andy to the airport for his flight back to Milwaukee and the two men say goodbye. Vann accidentally sets off the metal detectors in the airport and blames it on Andy. The story ends with a protesting Andy being led away by airport security for a body cavity search.

Question: Who does Peters suspect?
Answer: Peters suspects the dead agent and his partner Agent Derrick Vann.