To geography and trade

A hammer turned up in my back garden Friday night. I'd dismiss it as one of those random things that happens in Brent, but hammers don't tend to get over six foot garden walls by themselves. What if the police are on the lookout for a Willesden Hammer Killer, and this is the sort of thing that they really want the public to tell them? On the other hand the conversation could go something like this.

"Hello, I don't know if I should report this, but there's a hammer in my garden."
"Lots of people have tools in their gardens sir."
"Yeah, but this one's different. It's definitely not mine."
"You mean someone put it there?"
"Well, they don't get there of their own accord. Are you looking for a hammer killer at the minute."
"Are you saying you've hurt someone with it sir?"
"No, but someone else might have done."
"Has someone injured someone with it sir?"
"I was hoping you might know that."
"It's very important for crime to be reported sir. Are you afraid?"
"I am now. I'm just saying you might be looking for a hammer killer, and if you are, this might be important evidence. I'm just trying to help."
"We'll look into it sir. Can I have your name and address."
"Um, I'd rather you didn't."

Anyway, a search on BBC London shows three murders linked to Willesden in the past fortnight. None of them specifically mention hammers, but I'm going to put it in the shed, just in case.