(CNN) The killing in Belize of a US Marine Corps veteran and his Canadian girlfriend has left their friends and families struggling with an awful question: How could this happen?

So far, there has been no answer.

American Drew DeVoursney, 36, and Canadian Francesca Matus, 52, had been dating for several months when they went missing on April 25.

The couple was last seen at a popular oceanfront hangout -- Scotty's Bar and Grill in picturesque Corozal -- just a few miles south of the Mexican border. Matus, a realtor from Toronto who spent winters in tropical Belize, was scheduled to fly home the following day. DeVoursney was to return to the US a few days later.

But when a friend arrived the next morning to take Matus to the airport, he found her house locked -- and neither she nor DeVoursney could be found.

Grim discovery ends search

Volunteers and police combed the area after the friend reported the couple missing, but it wasn't until April 30 that Matus' white SUV was found about five miles from the bar. A day later, on Monday, their bodies were discovered about seven miles from the vehicle, according to a law enforcement source with knowledge of the investigation.

The couple had been strangled, their bodies dumped in a sugar cane field. The news was devastating to family and friends who had been desperately hoping the pair would be found alive.

"It's heart-wrenching and it's a roller coaster of emotions right now. I've never dealt with something like this in my life. It's horrible," said Nancy Rifenbark, a close friend of Matus.

"He was the greatest guy you'll ever meet," said DeVoursney's friend Brandon Barfield. The two men served together in Iraq. DeVoursney served two tours of Iraq as a Marine, and went to Afghanistan as a military contractor. "This is a true American," said Barfield.

Source: Duct tape found on couple's wrists

The law enforcement source said there was duct tape found on the couple's wrists but they were not bound together. After five days in the elements, the bodies were badly decomposed. Autopsies showed they died of manual strangulation -- and had blunt force trauma and broken bones in their necks.

The source said police are questioning two ex-pats who live near Matus because they were rumored to have had problems with the pair -- but police have not named them as suspects. Robbery is considered the most likely motive.

Neither Matus nor DeVoursney had wallets or ID with them when they were found -- but Matus' jewelry had not been taken. Rifenbark said the couple got along well with their neighbors and to her knowledge had no enemies.

Police resources stretched thin

While local police continue to investigate, Barfield is also looking for answers. He set up a GoFundMe page to raise money to help pay for a private investigator. By Wednesday, Barfield had already raised more than $8,000, and is hoping to raise $20,000.

While the US State Department reports crime in Belize is high, conviction rates are not.

"The majority of crimes remain unresolved and unprosecuted. A lack of capacity, resources, and training impedes the ability of local police to effectively investigate crime and apprehend serious offenders," according to the State Department's website.

"It's definitely not like the system in the US," said Rifenbark.

"It would be more comforting if there were officials from Canada and the US working on (the case) but I understand it's out of their jurisdiction," she said.

Tropical home away from home

Rifenbark was one of the last people to see the pair alive. She was at Scotty's bar the night they went missing. She said Matus was emotional that night -- sad to leave Belize, but excited to see her family back home. Matus owned a bayfront home north of Corozal. She spent time in Belize every winter to relax and take care of her property.

DeVoursney also owned property in Belize. His was an empty plot of land he bought with Barfield in 2010 with the money they had saved after getting out of the Marine Corps.

Neither had any connection to the country, but were lured there by what it had to offer. "Great diving, great fishing ... and by the way, it's English-speaking," said Barfield.

Plans for the property were always changing. Barfield said he and DeVoursney considered building a small B&B, or a bar, or perhaps running a scuba diving or fishing outfit.

The couple's families are now working with the US and Canadian officials to bring their bodies back for burial.