Billy disappeared with his brother, #link#4946dmmo Joel Hoag, and a friend, #link#4947dmmo Edwin Dowell. The boys were last seen on the south side of Hannibal, Missouri between 4:20 and 5:00 p. m. They were carrying shovels and a flashlight, and said they were going to explore Murphy's Cave, near the Highway 79 construction project. The three boys have never been heard from again. That day, the construction work resulted in a cave-in at Murphy's Cave. Because of the circumstances, authorities theorized the three boys were trapped inside the cave when it collapsed and couldn't get out. Extensive search-and-rescue efforts turned up no sign of any of them, however. In 2006, construction workers building a new elementary school on Highway 79 found a small cave about 50 feet long. Authorities checked it to see if the Hoag brothers or Craig were there, but they didn't find anything. Because nothing was ever found, there's speculation that the children weren't lost in the cave and something else caused their disappearances. A memorial marker for the boys has been placed in the vicinity of the cave. Billy, as described by one of his sisters to a reporter in 1967, likes to do everything his big brother Joey likes to do.