The Federal Bureau of Investigation is conducting an inquiry into the Oak Bluffs EMS and fire department, multiple sources familiar with the investigation have confirmed. The months-long inquiry began this past spring, with questions focused on the billing practices of the town ambulance service.

The FBI does not confirm or deny the existence of ongoing investigations.

But current and former members of the fire department confirmed that the FBI has been conducting interviews with members of the department.

At least four members of the department have been issued subpoenas to appear before a grand jury in U.S. District Court in Boston, last month and this month. All but one who spoke with the Gazette did so on condition of anonymity, because of FBI requests that they not discuss the matter publicly until they have testified before a grand jury. Several expressed concern about retribution.

Richard Michelson, a former lieutenant and 17-year veteran of the town EMS and fire department, said he was interviewed at his Oak Bluffs home by FBI agents on Dec. 26. According to Mr. Michelson, the interview lasted approximately 90 minutes, with questioning focused on ambulance billing practices. He said he has since received a subpoena to appear before a federal grand jury on Jan. 21.

Another current EMS employee who did not want to be named said the interviews revolved around ambulance finances, including billing, mileage, the role of the fire chief in billing and how information is sent to Comstar — a third-party agency used widely by Massachusetts towns, including Oak Bluffs, for ambulance billing. The ambulance service is operated by the fire department.

Selectman and board chairman Brian Packish said this week that he was aware of the investigation and had spoken last week with FBI agent Katherine Kelly, who supervises the agency’s Lakeville office. Town administrator Robert Whritenour also spoke with Ms. Kelly, Mr. Packish said.

“They have spoken with our chief of police and various members of the fire department,” Mr. Packish said. “We had a variety of questions because there hasn’t been any notification as to exactly what the investigation is in relation to. And basically her answer to any question asked was very consistent, and very simple: the FBI has an ongoing investigation and they do not comment on ongoing investigations. That is the extent of the information that we have.”

Mr. Packish said he and Mr. Whritenour had not been interviewed by the FBI, and as far as he knew, no one outside the fire department had been questioned.

He also said he was generally aware of the inquiry after

hearing “mumblings” this fall, but could not say whether it centered around EMS and fire department finances.

“The only information we have is that they have made public record requests. And these public records requests are for a variety of things, and they are not just specific to that,” the selectman said.

Reached by telephone this week, fire chief John Rose said he was on vacation and declined to comment.

In an email to the Gazette Tuesday, Mr. Whritenour said he could not comment on the FBI investigation or the public records requests.

“The FBI has specifically requested that the town not comment on their inquiry, so I won’t be able to make further comment on that,” he wrote.

On Wednesday this week, an email went out to all fire department employees from Mr. Whritenour requesting retention of all documents involving fire department business, including paper documents, emails and text messages.

Oak Bluffs EMS has had a right of first refusal on all off-Island ambulance runs since 1994, under an agreement with the Martha’s Vineyard Hospital. Proceeds from off-Island transfers go into the town ambulance reserve fund.

The town is the only one on the Island with such a reserve fund. The fund was created by an act of the state legislature in 1993 “to purchase and equip public safety vehicles for police and fire departments and for the payment of EMT compensation for ambulance transportation outside the county of Dukes County.”

The town uses Comstar, a Rowley-based ambulance billing service, to help coordinate complex insurance reimbursements for off-Island ambulance trips. Comstar handles billing for all four ambulance services on the Island and more than 200 municipalities in New England. Contacted by telephone Tuesday, Comstar CEO Rick Martin directed all questions back to the town. He declined to say whether the company had been contacted by the FBI.

The issue with ambulance billing briefly surfaced at a selectmen’s meeting on Sept. 24, when Mr. Whritenour told the board that Comstar had informed him there were problems with reimbursements from Medicare and Medicaid because the department had billed for ambulance runs that did not terminate at a Medicare-certified facility. In a video of the meeting, Mr. Whritenour said the town and Comstar looked back at the billings after rumors started circulating about a potential investigation into the town’s ambulance finances.

He explained that when an Oak Bluffs ambulance transports a patient to the mainland and another ambulance takes that patient to his or her final destination, Oak Bluffs cannot bill Medicare/Medicaid for the trip, and Oak Bluffs is left “holding the bag,” for the costs of that run. Federal guidelines also prohibit Oak Bluffs EMS from billing patients directly to recoup costs. Medicare is a federal program that provides health care coverage for the disabled and for people over 65 years old, irrespective of income. Medicaid provides health care coverage for low-income families and individuals.

Despite the rule, the town requested $37,535 in reimbursements for some non-Medicare/Medicaid ambulance runs between the years 2013 and 2015. The practice was stopped in 2016 when town officials became aware of the rule, Mr. Whritenour said at the September meeting.

The overbilled amounts totaled $26,084 for Medicare and $11,450 for Medicaid. Mr Whritenour said in an email this week that the town is now working with Comstar to credit back the overbillings.

“The town has directed Comstar to contact the Medicare folks to arrange for a credit on any of the overpayments we have discovered for trips that were transferred in Woods Hole, and they have done that. I am awaiting confirmation that the credit has been finalized,” he said.

Mr. Whritenour said he was unaware of any further problems regarding the town’s ambulance billings.

“We’re not aware of any other billing discrepancies at this time,” he wrote in a followup email.

In this week’s email to fire department employees, Mr. Whritenour wrote in part: “I’m sure you are aware of ongoing inquiries from outside agencies into departmental operations . . . To help us all do our part in addressing these matters I’m reaching out to you to request that you preserve any and all documents you may have pertaining to the Oak Bluffs fire department.”

The email went on to instruct employees to retain electronic documents — including emails, texts, Twitter, Facebook, Snapchat, or other social media communications — that mention or relate to the work they or others have done for the fire department “no matter how far back they may go.”

“We may be reaching out to you in the near future to request specific documents in connection with several active projects in which we’re engaged,” the email added.

The selectmen have met in executive session with their fire chief numerous times late this summer and fall, for reasons that have not been explained. Mr. Packish said he could not comment on the nature of the closed-door sessions. He also lamented the vagueness surrounding the investigation, and said hoped more information would be available soon.

“I wish I had more to offer, because the people in our town deserve the information, they deserve to know what is going on,” Mr. Packish said. “But due to the sensitivity of these matters, this is held in confidence for various reasons, and the FBI, I think, is well within their rights to not comment.”