Marinko Gosuljevic, Sinisa Jezovita and Darko Jaic admitted to having taken part in the kidnapping but not in the way described in the indictment filed by the Office for the Prevention of Corruption and Organised Crime.
Gosuljevic and Jezovita stressed they were not guilty of the first count, which charges them with associating, together with Ivan Matekovic and Stevo Smrcek, in a gang which planned to abduct children of several eminent business people.
Novica Petrac and Stevo Smrcek pleaded not guilty, while Ivan Bastalic said he was unable to enter a plea.
Four of the 10 accused, Hrvoje Petrac and brothers Ivan, Libero and Nikola Matekovic, are at large and are being tried in absentia. International arrest warrants were issued after them.
Fifteen witnesses are expected to be heard.