Task: Question Answering
Input (English): Passage: Richie Donovan works as a professional thief for Groznyi, a wealthy businessman, to pay off his debt for being smuggled into the U.S. as a child. He pulls off an initially successful diamond heist, but it is botched when he is involved in two separate car accidents. He is given one last chance to pay off his debt by going to Russia to steal a priceless antique cross, locked in a safe in a Moscow penthouse apartment. Richie and his Russian accomplices, brothers Peter and Yuri, recover the cross; but their elevator becomes stuck on the uncompleted 13th floor. Believing the police have stopped the elevator, the thieves take their fellow passengers hostage to negotiate an escape. They agree to send one hostage down; but, when the elevator doors open on the ground floor, the hostage has mysteriously been beheaded. 
The remaining hostages quickly divide into two groups: a Christian group consisting of Sonya, Helena and Katerina, who are later joined by Yuri, and another group consisting of nerdy Dmitry, beautiful Anna, and incompetent security guard Boris.
In the confusion, the Christian group seizes firearms and takes control, shooting Peter. Katerina is sent to stand guard over Richie and the remainder of the hostages, while Sonya takes Yuri to a chamber where he is to sacrificed by a wild man in armor named Alex. Yuri escapes, but he is impaled by one of Alex's traps, complete with disco music and lighting. In his rage, Alex kills Katerina, allowing Richie and the hostages to escape. They discover Alex's lair, where he has been watching everyone using security cameras. A photo reveals that Alex is the twin brother of Sonya, and they both believe themselves to be descendants of Ivan the Terrible. The group splits when Richie and Anna decide to chase after Alex, while Boris and Dmitry prefer to rig the room with various traps they have constructed and wait for Alex to come to them. 
Question: Who are the people who think the authorities are responsible for the elevator stopping, leading them to take hostages?
Output (English): Peter.