barking up the wrong tree

You're barking up the wrong tree if you think he took the money.

The police were barking up the wrong tree for months before finding the real suspect.

If you expect me to lend you money, you're barking up the wrong tree.

The researchers were barking up the wrong tree — the cure was something much simpler.

He spent years barking up the wrong tree before realising the real problem was elsewhere.

Are you sure you're not barking up the wrong tree with this theory?