A man in his 20s was arrested Monday on suspicion of killing a man whom he did not know in a residential neighborhood in northern Seoul, police said. The suspect, whose identity was withheld, was caught at around 1 a.m. for allegedly killing a man in his 70s in Gangbuk Ward on Saturday, according to Seoul Gangbuk Police Station. The police discovered the victim's body at around 7 p.m. Saturday while searching for him after receiving a report that he could not be reached. Investigators have so far determined that the two did not know each other prior to the incident. The suspect told the police that the killing was unintentional and occurred after the two got into an argument when their shoulders bumped into each other on the street, sources said. The police plan to seek an arrest warrant for the suspect after investigating the exact circumstances of the incident, including his motive.