"It was impossible to arrest former Balad chairman Azmi Bishara without removing his immunity," Deputy State Attorney Shai Nitzan said Monday.
In response to a request by MK Michael Eitan (Likud), Nitzan wrote that a petition to the Knesset to remove Bishara's immunity would have exposed the investigation and damaged it.
Bishara allegedly spied on behalf of Hizbullah during the Second Lebanon War by providing the guerrilla group with targets for their rockets, as well as classified military information.
In answer to a why the State Attorney's Office did not prevent Bishara from leaving the country after the investigation had been disclosed, Nitzan said that the law enforcement establishment did not believe that there was a reason to do so.
In response, Eitan said that it was unclear why Bishara was allowed to go to an enemy state, after he had already been investigated for the "most serious of charges - treason."
Eitan asserted that an MK indicted for treason did not merit immunity, Israel Radio reported.