A US couple whose boat was hijacked in the Caribbean last week are presumed to have died after being thrown into the sea, according to police in Grenada. Photo: BBC News

Ralph Hendry, 66, and Kathy Brandel, 71, both pensioners, have been missing since their catamaran was taken by three men on 19 February.

Police believe the suspects, who escaped from jail the day before, were attempting to head to St Vincent and the Grenadines.

All three have been found and arrested.

At a news conference on Monday, Royal Grenada Police Force Commissioner Don McKenzie said that "information suggests that while traveling between Grenada and St Vincent, they [the suspects] disposed of the occupants" of their catamaran, known as Simplicity.

"We have nothing conclusive to say that the individuals are dead," Mr McKenzie added. "We still hold out hope that in spite [of] what might be a low probability, that they would turn up alive somewhere."

Mr McKenzie added that the information that can be shared with the public is "quite limited" and that the investigation by Grenadian and Vincentian authorities remains ongoing.

Hours later, Royal St Vincent and the Grenadines Police Force spokesman Junior Simmons said the yacht's crime scene was "consistent with signs of violence".

"Several items were strewn on the deck and in the cabin, and a red substance that resembles blood was seen on board," he said.

Mr Simmons added that "the escapees have been co-operating with the investigation" and have already pleaded guilty to immigration-related charges.

According to the Salty Dawg Sailing Association - of which the missing couple was a member - Mr Hendry and Ms Brandel were "veteran cruisers" who were spending the winter months cruising the eastern Caribbean. They sailed to the region from the US state of Virginia last year.

The association was first alerted of the incident on 21 February that Simplicity had been found abandoned near St Vincent. The cruising skipper who found the vessel "found evidence of apparent violence".

"This is a very upsetting event and details are still unconfirmed by the authorities, but this does appear to be a tragic event," association president Bob Osborn said in a statement. "In all my years of cruising the Caribbean, I have never heard of anything like this."

A GoFundMe page set up for the family noted that Ms Brandel had "recently" become a grandmother.

"Kathy and Ralph, experienced adventurers, spent their retirement sailing aboard Simplicity, spending summers in New England and embracing the warmth of Caribbean winters," the page said.

The three escaped prisoners, aged 19, 25 and 30, had been in custody waiting to see a judge after being arrested on robbery with violence charges several months ago. The eldest detainee was also charged with one count of rape, three counts of attempted rape and two counts of indecent assault and causing harm, the Associated Press reported.

During the news conference on Monday, Mr McKenzie said that Grenadian authorities were working to determine whether the escape was the result of a "system failure" or "slip up".