Mr. Carpiak was the owner of the Mystery Spot in Broward, Florida.
On the first day of their investigation in Broward, Sam and Dean broke into the Mystery Spot after hours to find clues about the disappearance of Dexter Hasselback, who was last seen there. They were surprised by Mr. Carpiak, obviously fearful, holding a loaded shotgun and positioned to shoot them for trying to rob him. As Dean tried to calm him, the gun discharged and Dean was hit in the chest. Dean died in Sam's arms as Mr. Carpiak, apologetic, ran to call for help.
Sam awoke the next morning to find Dean alive and well and acting out everything exactly as he had the day before. Sam struggled throughout the morning to figure out why every detail was repeating. Remembering that Dean died because they broke into the Mystery Spot after hours, he strongly suggested to Dean that they go there during business hours. Dean grudgingly agreed. Once there, they interviewed Mr. Carpiak under the pretense of writing an article about the business. More important than the Hasselback disappearance to Sam at that point was that he suspected the Mystery Spot had something to do with what happened "yesterday." Because Mr. Carpiak was initially providing only evasive half-truths to their questions, Sam became angry and demanded that he tell them what was going on. Finally, Mr. Carpiak nervously admitted that he'd bought the business at a forclosure auction only months before and really knew nothing more; the police had already scoured the place for clues about the missing man. Dean hurried Sam away before he became any more upset.
Later, the brothers returned to the Mystery Spot and ended up binding and gagging Mr.Carpiak with duct tape while Sam took an axe to the interior, determined to take the place down to studs until he found some clue as to what was happening to them. Dean tried to calm Sam down while reassuring Mr. Carpiak that he would not be hurt. Dean finally decided to try to disarm Sam, and an offscreen struggle ensued. Mr. Carpiak let out a horrified scream as blood splattered his face.