The FBI has joined the probe into the double murder of a Virginia cardiologist in Belize and his fly-fishing guide.

Gary Swank, 53, was shot dead Sunday morning along with his tour guide, Mario Graniel, 53, while on a boat near the Ambergris Caye in San Pedro Town, Belize Live News reported.

San Pedro Commissioner of Police, Chester Williams, announced Wednesday that the US federal agents arrived in the country to assist in the investigation.

“There is certain expertise that we do not have in Belize and I have asked them to see how best they can assist us with those expertise and they have agreed,” Williams told reporters. “So, we are hoping that with the expertise they bring to the table, it will aid us significantly how we approach and deal with the investigation.”

Williams said local police have directed divers to search the area where the two men were gunned down for evidence.

Two suspects have been detained in connection to the fatal incident. The suspects — a woman and man — were not identified because no charges have been filed.

“Certain things were retrieved, so yes we have made some progress where that is concerned,” Williams said.

Earlier in the week, authorities said there was a female suspect in custody with close ties to the slain tour guide. Investigators suspect that Graniel was the intended target while the visiting doctor was “collateral damage,” according to Belize Live News.

Police announced on Thursday that 23-year-old Christian Espat was wanted for questioning in the case. The alleged gangster denied any involvement and has since turned himself in to police, according to the report.