Was this legal?

An anonymous submitter wants to know if what happened to him was legal. What do you think?

I just went outside to let my dog in because she was barking and going crazy. When I got back inside my wife informed me that the dog was barking because the police were snooping around my property. I went outside to find two officers entering my backyard without my consent or permission. When I tried to ask the officer what he was doing, he looked at me and said he was looking for someone and kind of waved me back. I went around back to find another officer opening the door to my shed and looking through it. I asked what they were doing. They told me they were looking for a guy with a big gray handlebar mustache and to give them a call if I saw him, then just walked off. How is that legal?!?!