Kathryn Bolkovac is a police officer from Lincoln, Nebraska, who accepts an offer to work with the United Nations International Police in post-war Bosnia and Herzegovina for a UK company, Democra Security (a pseudonym for DynCorp International). After successfully advocating for a Muslim woman who experienced domestic abuse, Kathryn is appointed head of the department of gender affairs.
Raya, a young Ukrainian woman, and her friend Luba are sold to a Bosnian sex-trafficking ring by a relative. Raya escapes with Irka, another girl forced into prostitution, and they are sent to a women's shelter for victims of human trafficking. While investigating their case, Kathryn uncovers a large-scale sexual slavery ring utilized by international personnel (including Americans). She persuades Raya and Irka to testify against their traffickers in court, guaranteeing their safety; however, an indifferent UN official drops Irka at the border between Bosnia and Serbia when she cannot produce a passport. A corrupt peacekeeper tips off the traffickers, and Raya is recaptured and tortured. Although Kathryn rescues Irka from the woods, the latter is too afraid to proceed with the trial.
When she brings the scandal to the attention of the UN, Kathryn discovers that it has been covered up to protect lucrative defense and security contracts. However, she finds allies in her investigation: Madeleine Rees, head of the Human Rights Commission, and internal-affairs specialist Peter Ward. When one of the girls found dead, Kathryn sends an email to fifty senior mission personnel detailing her findings; she is then fired from her job. She and Ward acquire evidence of an official admitting the scandal before she is forced to leave the country, and she brings it to the BBC News. The final credits note that after Kathryn's departure, a number of peacekeepers were sent home (although none faced criminal charges because of immunity laws), and the U.S. continues doing business with private contractors such as Democra Security (including billion-dollar contracts in Iraq and Afghanistan).

Question: Who tips off the traffickers?
Answer: A peacekeeper
Alternative answer: A corrupt peacekeeper