An officer of Bulgaria's State Agency Technical Operations (SATO), an institution in charge of applying special investigative techniques such as surveillance and interception, has been arrested for betrayal, officials said Tuesday. Security services heads told a joint press conference that Antoaneta Parvanova, who worked at the agency since 2010, informed people for money when they were tapped or monitored. Parvanova has impeded a lot of investigations and betrayed information repeatedly, Sofia City Prosecutor Hristo Dinev said, adding that she was arrested on Monday. Her son-in-law, involved as an intermediary, and two "clients", were also arrested on Monday, he said. Prosecutors had evidence that individuals have paid "monthly cash subscription" in exchange for receiving check whether their phone was monitored, Dinev said. The "subscription fee" ranged from 500 to 3,000 BGN (some 350 to 2,100 U.S. dollars), according to Borislav Sarafov, Deputy Chief Prosecutor. Parvanova was discovered thanks to the new internal security system, implemented by SATO after its removal from the Ministry of Interior, the agency chairman Tsvetan Kitov said. SATO was separated into an independent state agency under the council of ministers last July, after a scandal erupted in March when Sergey Stanishev, leader of the Bulgarian Socialist Party, said that a group in the Interior Ministry had illegally tapped politicians, businessmen and public figures from September 2009 to March 2013.