When Phil Roy signed on for Sunday’s marathon run across a corner of New Mexico’s high desert — memorializing the 600-plus Americans who died during the Bataan death march — the Auburn man didn’t know about his family connection.

Then he heard about his Great-Uncle Edgar.

Caribou native Edgar Romeo Roy was among the GIs presumed killed along Bataan’s three-day, forced march in early 1942. For 80 miles, the captured Allied soldiers left behind during their retreat in the Philippines were beaten and deprived of food and water. Some were bayoneted or summarily shot by their Japanese captors.

On May 7, 1942, the Army reported Edgar Roy as missing in action. Almost four years later, as the Japanese officers who led the march were tried and executed for war crimes, Roy was officially declared dead. His name was added to a stone tablet in Manila.

“I had no idea,” said Phil Roy, a master chief in the Coast Guard. The 40-year-old non-commissioned officer had joined the run to challenge himself. He knew of the march, but he didn’t know he had a relative in it. “It was amazing, the coincidence.”

So, he researched all he could.

“I tried to get a copy of his military record,” he said. He failed. A 1970s fire in St. Louis destroyed a Department of Defense archive. He talked with family here in Maine. He managed to collect a few details and Edgar’s photo from Caribou High School.

The image — of a teenager in a coat and tie — will accompany Roy in the desert on Sunday. He printed up T-shirts. He distributed them among family and he’ll wear one beneath his fatigues when he begins his own arduous march Sunday morning.

The run is a full, 26.2-mile marathon set for the White Sands Missile Range in southern New Mexico. The course snakes out into the hilly desert. And Roy will be wearing combat boots.

“It’s mostly off-road,” he said. “It’s through the desert, and it’s sugary sand. For every step you take, you lose a quarter step. It’s pretty brutal. And they were nice enough to put a 2,000-foot elevation gain at the 13-mile mark.

“It’s definitely a butt-kicker,” said Roy, an experienced runner. “I normally finish a marathon in just under four hours. Given the conditions, the sand and the elevation and running in boots, I’m forecasting between a six- and seven-hour finish time.

“I’ll be happy if I can achieve that,” he said.

He’ll have the support of family at home.

On Thursday, a box of the T-shirts arrived at the Lewiston home of Roy’s aunt, Barbara Dube. Besides the photo of Edgar, the T-shirt carries the POW-MIA logo, the long-lost soldier’s name and the words, “In loving memory.”

Minutes after receiving the T-shirts, Dube took one to her father (Phil’s grandfather) Philip Roy Sr.

The elder Roy, a hero in World War II in Europe who earned the Silver Star, the Bronze Star and the Purple Heart, beamed at the T-shirt. At 88, he has slowed, but he talked about his grandson with pride.

The younger Roy called his grandfather “the most honorable guy I know. I want him to know that we’re not forgetting about him or his brother,” the runner said.

Dube has come to expect such thoughtfulness from her nephew, Phil.

“He doesn’t miss a birthday or Mother’s Day,” Dube said. After he graduated from Edward Little High School in 1991, he went directly into the Coast Guard. He would eventually become a salvage diver.

“He seemed to rise through the ranks so easily,” she said.

And though he has been stationed in many places, he still considers his residence to be here, in Maine.

“This march has become another way of honoring his family,” Dube said.

[email protected]