Kim Ki-jong, who attacked the US ambassador to South Korea Mark Lippert at a public forum, is carried on a stretcher off an ambulance as he arrives at a hospital in Seoul March 5, 2015.[Photo/Agencies]

Though Kim insisted that he had no intention to kill the envoy, the police said Kim attacked Lippert several times with a 25-centimeter-long knife, which is the indication of his intentional murder.

About 25 police investigators raided Kim's home and office earlier in the morning after receiving a search warrant from the court, seizing documents and hard discs from there. The police are also analyzing his cell phone records.

The police are investigating into whether Kim violated the National Security Law, which bans South Koreans from publicly sympathizing with the Democratic People's Republic of Korea (DPRK).

According to the police, Kim visited the DPRK seven times between 1999 and 2007, and tried to erect an altar for late DPRK leader Kim Jong Il in central Seoul in December 2011.