Downer was reported missing on May 5, 2009. A neighbor contacted the El Cajon Police Department and asked them to check on him, as the neighbor hadn't seen him in over three weeks. The last contact with him was on April 10, his birthday. When investigators went to Downer's home, they found it locked with no cars in the driveway. Looking through a window, they noticed spoiled food left out on the counter and decided to force entry. Downer wasn't inside and there were no indications of foul play.

One of Downer's vehicles, a maroon 1995 Chevrolet Lumina with the California license plates number 3NOF507, was towed from the Oak Oasis County Park in the 12600 block of Wildcat Canyon Road in Lakeside, California on April 9, a little less than a month before his disappearance was reported. An extensive search of the park turned up no sign of him. Downer's family stated he had problems with his balance but was otherwise in good health at the time of his disappearance. He apparently took regular hikes. His case remains unsolved.