As authorities hunt for clues in the mysterious murder of North Korean leader Kim Jong Un's elder half brother, Kim Jong Nam — reportedly at the hands of agents from the North — ties to Japan by both brothers may figure prominently in the audacious killing.

Kim Jong Nam was killed Monday morning at Kuala Lumpur International Airport as he was readying to board a flight to the Chinese enclave of Macao, South Korean authorities confirmed Wednesday. News of his dramatic death first emerged late Tuesday.

But while South Korea's spy agency said that it suspects the North to be behind the murder, it did not directly blame Pyongyang. According to the South's Yonhap news agency, however, National Intelligence Service (NIS) Director Lee Byung-ho told lawmakers that for the past five years Pyongyang had been attempting to assassinate Kim Jong Nam, who had been under the Chinese government's protection.