The Mireles-Garcia brothers rarely missed a day of work over a decade at a dusty concrete casting factory in Dumfries, relatives said, sending part of each paycheck home to a rural Mexican town to pay for their parent’s medical bills and sister’s college.

Then on May 10, 2010, after another workday and a call to wish their mom a happy Mother’s Day, Manuel and Alberto vanished. Their neat apartment in Triangle was left as if the pair, in their early 30s, had simply run out for an errand.

Their whereabouts were unknown until two weeks ago when Fairfax County police announced that two sets of skeletal remains — found over an eight-month period in the woods in Lorton — belonged to the brothers. Both skeletons bore signs of foul play, police said.

In the two years since the men went missing, their father died and the family’s hope of finding Manuel and Alberto alive has dissolved into sorrow but one thing has endured: the mystery of how two brothers — who had no criminal records and showed no obvious signs of trouble — disappeared and ended up slain in a corner of Fairfax County.

“We really don’t have a working theory in this case,” said Officer Bud Walker, a Fairfax County police spokesman. “We don’t think they were involved in anything nefarious. They were regular working guys.”

The investigation began on a quiet Lorton road and moved down I-95 to Prince William County, where the brothers lived and were last seen, and then on to Durango, Mexico, where a family grieves for them and desperately wants to find the killer. It is a story that offers few clues, but raises even more questions.

A man was driving down Furnace Road in Lorton around 8 p.m. on July 12, 2010, when he spotted a deer not far from the Fairfax County landfill, police said at the time. He stopped to snap a photo and stumbled upon a skull and bones at the edge of the woods. The remains were later identified as Manuel’s.

Manuel wore a chain necklace with a stone, heart pendant and “evil eye” talisman, police said. He also had on a green American Eagle track suit and a T-shirt with a picture of a hot rod.

Eight months later, and a half-mile away, a pedestrian came across a second set of remains at the base of a rusting trestle bridge that spans a neck of the Occoquan Reservoir, police said. The bones were later identified as Alberto’s.

Both sets of remains showed blunt trauma to the upper body and Virginia’s medical examiner ruled the deaths homicides, police said. Relatives said the brothers had no connection to the area where they were found, but spent nearly all their time about 15 miles south in Prince William County, where they lived and worked.

Manuel and Alberto immigrated to the United States about 10 years ago, eventually showing up on the Triangle doorstep of Horacio Garcia, their uncle, relatives said. The pair had no home or work, but wanted to improve their lot and help support their family, relatives said.

Garcia became like a surrogate father, letting Manuel and Alberto live under his roof for more than five years and helping them find work with his own employer: Arban Precast Stone in Dumfries, relatives said. The brothers were good and dedicated workers, according to their boss.

Manuel and Alberto earned enough to move into their own apartment, a squat white and teal building near the Marine base at Quantico on Fuller Heights Road. Though they lived and worked together, they were quite different, relatives and friends said.

Alberto liked jeans, Mexican music and the movie “Scarface.” Manuel preferred the preppy look of Nautica, Lady Gaga and Marilyn Monroe. The differences extended to their statures: At 5 feet 9 inches, Alberto was five inches taller than his brother.

They were both reserved, drank little and had few visitors at their apartment, relatives and neighbors said. They enjoyed going to Potomac Mills on Sundays, but not to clubs on Saturday night. Relatives said there was no sign the two used drugs or were involved in other illegal activities.

Ruben Garcia, Horacio Garcia’s son, said he saw Alberto two days before he disappeared. His cousin had stopped by his Triangle apartment to borrow some movies. They made plans to catch a film the next weekend. Garcia said Alberto and Manuel were like brothers to him, but he had not seen as much of them in recent years.

“I’m going to make time,” Garcia recalled telling Alberto. “We are going to hang out a little more.”

He never made good on that promise.

“Ever since they disappeared, everyone is spooked. I couldn’t really sleep at night for awhile. I thought whoever got them would come into my room and get me,” said Ruben Garcia, who used to live in the same apartment building as the brothers. “I know them pretty well. I think if they were into something illegal I would know.”

Alberto and Manuel went to work on Monday, May 10, 2010 and seemed normal, co-workers said. At some point, they called their mother, who had suffered a stroke, to wish her happy Mother’s Day in Mexico, relatives said.

After work, Victor Arroyo, a co-worker, said he spotted Alberto near a 7-11 behind the brothers’ apartment building. Arroyo, who was planning to take a vacation to California, said he stopped and chatted with Alberto about the trip. He said Alberto had cleaned up and put on fresh clothes after work, as if he were planning to go out. The pair parted ways. Arroyo said police told him he was the last person to report seeing Alberto alive.

Family members reported the pair missing on the morning of May 12. Officers found the brothers’ vehicles parked at their apartment complex. A search of their apartment turned up no additional clues, but their keys and identification were not located, police said. Police said they also reviewed the amount of money the brothers sent to Mexico, and it was consistent with their work in the factory.

After the remains were discovered, Walker, the police spokesman, said detectives had a hunch the bones belonged to the brothers after poring over missing persons reports. A detective flew to Mexico to gather DNA from family members and it was tested against material collected from the sets of remains, producing a match, Walker said.

Police declined to discuss other details of the case, saying they were still following up on leads.

After a recent shift at the cement casting factory, Horacio Garcia spoke about his nephews. He wore a stained sweatshirt and looked pained as he talked — a co-worker said he feels partly responsible for Manuel and Alberto’s disappearance. They were his sister’s children and he invited them into his home.

Just as he helped them in life, Garcia is hoping to do the same in death. He is planning a service for the brothers and will ship their remains back home to Durango to be buried, if he, his family and his co-workers can raise the necessary $1,300.

“I don’t know what happened,” Garcia said,“but I know my nephews and they were beautiful people.”