According to police, a grandfather was shot and killed on Monday on the New York subway after he intervened to try and end an argument over loud music.

In a statement, police say the victim, identified as 45-year-old Richard Henderson, was shot in the back and shoulder as he was riding the subway home Sunday evening.

In a case that highlights the sporadic nature of gun violence in the US—a nation where there are more firearms than people—authorities have not made any arrests.

Over five million people use New York's antiquated subway system every day, and this incident was just the most recent in a string of violent ones.

After attending an American football game at a friend's house, Henderson was returning home to his family, according to a report from Henderson's brother on CBS New York.