SANTO DOMINGO, Dominican Republic — A New Jersey man died last week while staying at a resort in the Dominican Republic, becoming at least the ninth American tourist to die under mysterious circumstances in the last year while visiting the small Caribbean country.

Joseph Allen, 55, was found dead in his room Thursday at the Terra Linda Resort in Sosua, where he was celebrating a friend's birthday, his family confirmed to NBC News. An autopsy report provided to NBC News by a police source in the Dominican Republic showed Allen had prior heart issues, but an official cause of death is still undetermined pending a toxicology report.

Allen's sister-in-law said that the family was scrambling for answers.

"My brother was a hard worker," Allen's brother, Jason Allen, told NBC New York. "He taught me a lot about sacrifice. ... He taught me so many things about being a man. He was selfless."

Joseph Allen of Avenel, New Jersey, died last week while staying at a resort in the Dominican Republic, his family confirmed to NBC News Wednesday. Courtesy of Allen Family

The night before his death, family members said Allen — who has a 23-year-old son — complained to friends about the heat and went back to his room to take a shower and lie down.

"The maid opens the door, screams, slams the door. My brother is on the floor dead, between his room and the bathroom," Jason Allen said.

Jason Allen said he doesn't know who is to blame for his brother's death but wants it investigated.

"I'd rather not guess because you will drive yourself crazy with that, but I do think something is off, and I think it needs to be investigated no matter how much money or how much time it is," he said.

A representative for the Terra Linda Resort was not immediately available for comment.

A number of other families have also reported stories of their relatives mysteriously dying while staying at resorts in the Dominican Republic.

Leyla Cox, 53, an MRI technician from the New York City borough of Staten Island, was staying at the Excellence resort in Punta Cana when she died June 11, just a day after her birthday, according to her son. Will Cox said he still does not know his mother's cause of death and has not had the chance to mourn properly as her remains haven't been returned home.

According to him, a representative for the U.S. Embassy said a toxicology test would not be conducted on his mother's body because the machines were broken.

Robert Bell Wallace, 67, died while staying at the Hard Rock Hotel and Casino in Punta Cana on April 12. Wallace's family asked for privacy and has not confirmed the circumstances of his death to NBC News.

In May, Miranda Schaup-Werner and a couple, Nathaniel Edward Holmes and Cynthia Ann Day, died over a five-day period at the Bahia Principe resort in La Romana.

Holmes and Day were found dead in their room. Pulmonary edema — excess fluid in the lungs — was listed among the causes of death for the couple in preliminary reports.

The FBI, which is investigating the three May deaths, said further toxicology results on the Americans could take up to 30 days.

Jerry Curran, 78, checked into the Dreams resort in Punta Cana on Jan. 22, and died three days later, his daughter, Kellie Brown, told NBC affiliate WKYC in Ohio. The State Department confirmed Friday that an American died in the Dominican Republic in January.

“He went to the Dominican Republic healthy and he just never came back,” Brown said.

Authorities told the family that one of Curran's causes of death was pulmonary edema, "which seems to be common in everyone else who's passed that we're learning about,” Brown said.

A statement from the Dreams resort said that the hotel management has "no evidence that this unfortunate incident was the result of anything other than natural causes."

At least two other Americans, Yvette Monique Sport and David Harrison, died at resorts in the Dominican Republic in 2018.

The U.S. ambassador to the Dominican Republic, Robin Bernstein, said in a statement that the safety of U.S. citizens "remains our highest priority."

"These incidents are tragic and we offer our deepest condolences to those personally impacted," Bernstein said.

Rappleye reported from Santo Domingo, Madani from New York.