CHEYENNE - When graduate student and lab instructor David Pearson phoned in sick Nov. 3, no one in the University of Wyoming Geography Department thought much about it.

The call turned out to be the last anyone heard from him - and fellow students, instructors, family members and police are baffled as to why.

A search of his Laramie apartment revealed no sign of forced entry and nothing unusual, except that his dark green 1999 Ford Escort, his mountain bike and his laptop were missing.

"We're all just at a total loss, frankly," John Allen, chairman of the department, said Monday. "None of us can figure out what's gone on with Dave."

Pearson is 47 and single, and Laramie police were initially reluctant to search for him, according to his father, Charles Pearson of Huntsville, Texas.

"One cop said, 'Well, he just probably went to Las Vegas,'" the elder Pearson said. "Well, I know my son. He wouldn't go to Las Vegas … It's totally out of character."

Allen agreed.

"He was very responsible," the professor said. "He had a military background and no indication of any kind of difficulties. He was doing a really good job for us and reliable in the lab."

It's been a trying month for Charles and Barbara Pearson. David's disappearance occurred just before his sister, Lisa, 49, underwent emergency surgery in Texas for a ruptured spleen. She was upgraded from critical to stable condition Sunday.

"We kept leaving e-mails and voice mails on his cell phone and he never responded," Charles Pearson said. "He and his sister are tighter than bark on a tree … We knew something was wrong."

David Pearson grew up in the Houston suburb of Alief, served five years with the Marines, worked as a helicopter mechanic then hired on with oil industry giant Schlumberger Limited. He worked seven years as a machine operator but was laid off after back surgery.

He decided to attend college, receiving a bachelor's degree in geography from Sam Houston State this past May. He enrolled at UW in August to begin a two-year master's program.

Because of the high price of gas, David bought a mountain bike and recently started riding in the hills near Laramie, his father said.

David is a non-drinker and non-smoker, stands about 6 feet tall and weighs 180 pounds. He wasn't in great physical shape, at least not for an extended ride in the mountains, Charles said, and he thinks his son might have accidentally gone over a cliff in either his car or on his bike.

Fellow students and volunteers have checked trailheads in the Medicine Bow National Forest but have found no sign of Pearson, his car or his bike.

"His mother and I feel like, if you find his car, you'll find him," Charles said.

Laramie police Cmdr. Jeff Bury said officers were checking the national crime information computer to see if David's car had been stopped somewhere. The department is working with the UW Police Department and periodically checking the man's apartment and leaving messages, he said.

The officer heading the investigation was off-duty Monday and not available for comment, a dispatcher said.

Meanwhile, the UW Geography Department is putting up posters asking for the public's help.

"We've wracked our brains," Allen said. "He just inexplicably disappeared and we have not a clue as to where he is."

The license plate of David Scott Pearson's 1999 Ford Escort is Wyoming 5-230Z. Anyone with information is asked to call the Laramie Police Department at (307) 721-2526.

Capital bureau reporter Robert W. Black can be reached at (307) 632-1244 or robert.black@casperstartribune.net.