After passing Svartmangatan he came to a small square. By coincidence, it was the same square as the location of the factory where M worked earlier that day. One theory is that the man could have been on his way to see his brother. M was discovered by the man who immediately understood what it was all about. An intensive fight started accordingly and they both knew they were fighting about the same person. The fight went out of control and people fled the place for their safety.
After some minutes M killed the man using the weapon and the 30 arrows he just bought. The man did not expect any weapons to be used so he was unarmed. So, he was simply slaughtered in an unfair game with only one possible outcome. M buried the man afterwards right in the middle of the square. Then he wanted to destroy everything: the body, the evidence, the memories, the factory etc and he had some good explosives in his pocket.
But the matches were scrambled!