Joseph Vill's Death in the Battle of Philadelphia

Joseph Vill was from Philadelphia. He died at 23 years old the day after the invasion. They said clearing the water of mines when he got shot by a sniper. How do they even know that though? Well, that was the next thing. It's possible because who would have known like, there's no one you think they sit there and interview every person in the water next to him at the time.