Hey kiddo, have you ever heard of something called lead? It's a metal that can be found in different things like old paint, gasoline, and even soil.
In the past, people used to add lead to gasoline and paint products. This was a problem because when people would breathe in the lead or touch it, it could get into their bodies and cause problems.
Now, some people think that lead could have a bad effect on people's brains, which could cause them to do bad things like commit crimes. This idea is called the "lead and crime hypothesis".
There's some really smart people who have been studying this idea and they've found that places that had a lot of lead in the past also had higher crime rates. They think this might be because lead can affect the development of the brain, especially in young children.
But it's still something that needs more research and testing. So scientists are still trying to figure out if lead really does have an effect on crime.