The investigation will focus on the questioning of witnesses, the chief of the County Court's investigating department, Mirjana Rigljan, said on Friday, but declined to reveal the number of witnesses who will be heard.
Speaking to Hina, a source at the County State Prosecutor's Office only confirmed the office had proposed the investigation, but declined to speak further of the case, saying it was classified as a state secret.
Under the Criminal Code, unauthorised surveillance committed by an official is punishable with imprisonment ranging from three months to three years.
According to the media, the charges pressed against Turek stated that he had added the telephone numbers of several persons to a Supreme Court order which approved tapping of phone of retired Colonel Miro Lace.
The charges were pressed in late November and the Zagreb police interviewed Turek earlier this month. He told the press after the interview he did not expect an indictment to be issued against him because he did not see anything contentious in what he was suspected of.
"I don't see how you can unlawfully tap someone's phones if you have a valid written order," he said, adding the order dated from 2001, when surveillance was being approved by the then Interior Minister Sime Lucin.
Turek also claimed that the police interview did not address the alleged addition of names to the Supreme Court order. He labelled such accusations against him as incorrect and "insinuations", and that the "political charges" were pressed against him by his successor as POA chief Josko Podbevsek.