State prosecutors in Seoul courtroom said they requested the heavy sentence for Song, professor at Muenster University in Germany, accusing him of violating the anti-communist National Security Law, Korea Times reported. A verdict is expected on March 30.
The 59-year-old professor was charged for acting as a member of the Politburo of North Korea's Workers Party and spreading the North's Juche, or self-reliance ideology on orders by Pyongyang.
Song allegedly visited North Korea more than 20 times since 1973 and received up to $104,000 from the North Korea.
The professor admitted that he had joined the Workers' Party in 1973 and received money from Pyongyang, but he denied he had been formally elected as a Politburo member or participated in activities benefiting North Korea while residing in Europe.