The authorities in Grenada said on Monday that they believed an American couple who had been traveling in their catamaran in the Caribbean were hijacked by three escaped prisoners who “disposed” of them last week.

The couple, Ralph Hendry and Kathy Brandel, had departed from Virginia and were spending the winter cruising in the Caribbean, where they went missing while sailing off Grenada. On Feb. 21, their boat turned up empty in neighboring St. Vincent and the Grenadines.

On Monday, the Royal Grenada Police Force confirmed that three prison escapees in Grenada made their getaway after they hijacked the catamaran, called Simplicity, with Mr. Hendry and Ms. Brandel aboard.

“Information suggests that, while traveling between Grenada and St. Vincent, they disposed of the occupants,” Commissioner Don McKenzie of the Royal Grenada Police Force said at a news conference on Monday.

The police would not say explicitly that they believed Mr. Hendry and Ms. Brandel were dead but that they were still considered missing.

“We have nothing conclusive to say that the individuals are dead,” he said.

“What I can say to the family is my condolences,” adding that he was “still hoping for as what I consider a positive outcome which is, we still have the hope that a worst-case scenario will not be a reality.”

According to the Salty Dawg Sailing Association, a nonprofit that brings together sailing and cruising enthusiasts, a skipper notified it on Feb. 21 that a member’s yacht, Simplicity, was found anchored and abandoned off a beach on the southern coast of St. Vincent.

The skipper boarded the catamaran and noted that its owners were not onboard, the association’s statement said. The missing boat owners were identified as Mr. Hendry, 66, and Ms. Brandel, 71, by the association and Ms. Brandel’s son, Nick Buro.

Mr. Hendry and Ms. Brandel, who were married for 27 years, were experienced sailors who lived on their boat.

They recently completed their sailing club’s “Caribbean Rally” — cruising from Hampton, Va., to the island of Antigua to end 2023 with a celebration — and they were spending the remainder of the winter cruising the Caribbean, according to a statement from the club.

The association said that it had a tracking map to follow members’ boats and that it showed that Simplicity was anchored in Grenada before docking off St. Vincent.

Separately, the Royal Grenada Police Force said in a Feb. 22 statement that three men who escaped from a prison in Grenada on Feb. 18 made their way to St. Vincent using a yacht that had been docked in the St. George area of Grenada.

The prisoners were recaptured on Feb. 21, the same day that the couple’s vessel was found.

The authorities identified the prisoners as Trevon Robertson, 19; Abita Stanislaus, 25; and Ron Mitchell, 30.

They had been previously charged, jointly, in a violent robbery case in December. Mr. Mitchell also faced various separate charges that included causing harm, indecent assault and rape, the Grenada police said.

It was not immediately clear on Monday what charges they may face regarding the couple’s disappearance.

The police commissioner said a team of investigators from Grenada and the St. Vincent and the Grenadines Coast Guard were dispatched to St. Vincent to help in the investigation.

In a joint family statement on Saturday, Mr. Buro and Bryan Hendry, Mr. Hendry’s son, thanked the cruising community for its support and help in the search but asked them to stand down.

“We also want to applaud the St. Vincent authorities for their quick actions in securing Simplicity and their brave, swift response that led to the apprehension of three dangerous fugitives,” according to the statement.

Bob Osborn, president of the sailing club, described the couple as warmhearted and capable and called their disappearance “a very upsetting event.”

A GoFundMe page started by a family friend described Mr. Hendry and Ms. Brandel as “experienced adventurers” and said they had “spent their retirement sailing aboard Simplicity, spending summers in New England and embracing the warmth of Caribbean winters.”