The suspect in his 60s accused of stabbing main opposition Democratic Party(DP) Chairman Lee Jae-myung was referred to the prosecution on Wednesday morning on charges of attempted murder.

The suspect, identified only by his surname Kim, told reporters that he is sorry for causing concern as he was escorted into a vehicle at a police station in the southeastern port city Busan when asked if he had anything to say to the DP chair.

Asked why he wrote a memo of "excuse" ahead of the stabbing, Kim told the reporters to read it to get a better understanding of his motive.

Asked whether he had planned the crime alone upon arrival at the Busan District Prosecutors' Office, Kim said "yes," adding he had only asked a man in his 70s suspected of aiding and abetting to send the "excuse" memo via mail.

Kim was placed in pretrial detention on charges of attempted murder after stabbing Lee in the neck with a camping knife in Busan last Tuesday.

The police plan to announce the outcome of their investigation on Wednesday afternoon.