Middle grade thriller where a neighborhood kid is killed by her brother, published pre-2005

I've been trying to remember what this book was called on and off for yeeears!

• I read it at some point between 2000-2005 and it was contemporary, so probably not published before the 90s
• The protagonist/main POV was a boy
• There was a group of neighborhood kids and they possibly could have been playing in a storm drain or went under the street through a manhole or something??
• There may have been a thunderstorm or some kind of power outage/flashlight dying situation that leaves them temporarily in total darkness
• While it's dark, one of the kids, a little girl, is killed, and the plot of the book is the main character trying to figure out who killed her
• The big reveal at the end of the book is that the girl's own brother was the one who killed her, and I think he gets arrested??

I picked the book up in my school library so I don't think it would be super obscure, but I stg I've googled every combination of words I can think of that are related to this book and I've never been able to find it.