It was the sort of stuff one would expect to see on a TV mystery series. A few days ago, an employee of a dry cleaning establishment on West Stadium Boulevard in Ann Arbor, Mich., happened to be checking the pockets of a sport coat that a customer had brought in, prior to putting the garment in the fluid. And there in one of them was a piece of paper on which was written this note: "You have committed a murder, but no one believes it. All I can do is kill myself. Then everyone will see what you have done. Your wife, Alice." Let's say you were that employee: What would you do? Well, you might have assumed the note was connected to a gruesome crime and telephoned the police. Indeed, that's just what the staff at the shop did. The cops responded, and it wasn't long before the customer was tracked down and questioned. And that's when detective Brian Zasadny discovered that the situation was nothing like what it appeared to be. The customer turned out to be a professional actor. And the note was a prop in the play "The Retreat from Moscow," a former Tony Award-nominee in which he has one of the three roles. It is being featured this month at the Performance Network Theater in the city.