Dukes County sheriff Michael McCormack confirmed this week that he called for state police to investigate allegations of officer collusion in two separate inmate beatings at the Dukes County House of Correction.

Mr. McCormack asked for the investigation last November after an inmate charged that correctional officers had been involved in two assaults last year. He said the investigation could be concluded by the end of this month.

"On or about Nov. 11 the investigative arm of the district attorney's office started a formal investigation," said Mr. McCormack. "These are very serious allegations. If they prove true, it could result in criminal charges and discharge for the officer or officers."

"State police detectives assigned to our office are investigating this, and they are taking witness statements," said Michael Trudeau, the first assistant Cape and Islands district attorney. "Once all of the interviews are complete, they will be reviewed to determine if charges need to be made."

News of the investigation was first reported in the Boston Globe last Friday.

Inmate Alan Thistle, 52, of South Boston, drew attention to the beatings in detailed letters written to the Globe and to Scott Harshbarger, the former attorney general who is chairman of a special commission investigating the state prison system.

In his letters Mr. Thistle chronicles the attacks, and includes charges of intimidation and harassment by several officers and official indifference to his complaints.

Sheriff McCormack this week said the assaults occurred in June and September of last year. In the first incident, an inmate attacked former inmate Paul Garcia, 54, of West Tisbury; in the second incident the same inmate attacked Mr. Thistle.

Mr. McCormack would not discuss the details of the beatings.

"No one on our staff saw either of these assaults take place," he said. He added that neither Mr. Garcia nor Mr. Thistle wanted to press criminal or civil charges.

Mr. McCormack said that in both cases internal disciplinary action was taken against the inmate who initiated the attacks.

At the time of the beating, Mr. Thistle was being held at the jail temporarily at the request of the Suffolk County district attorney's office.

Sheriff McCormack said the majority of inmates who are housed at the Edgartown jail have committed crimes on the Island, with about four at any time being held at the request of district attorney's offices in other areas. The decision to take on additional inmates is made at the sheriff's discretion.

"Often those requests come because of the inmate's former occupation - maybe he is a police officer or a lawyer; the nature of the crime committed; or if the inmate is cooperating with the district attorney," said Mr. McCormack. "They are often people who for one reason or another would be unable to survive within the general population of other jails."

The county jail accepts prisoners who are sentenced to serve up to two and a half years. It cannot accommodate women and has a designed capacity of 18 inmates; the average population, however, is about 30.

The Dukes County House of Correction was first constructed in 1873 on the site where the county courthouse now stands. It was later moved to its present location on more than an acre of land on Upper Main street.

The two-story building originally contained 12 single cells, at a time when the inmate population was at the most two. Today the physical building has deteriorated significantly; the brick and granite cells are attached to the wooden structure of the original house frame, and the original electrical wiring is still in place.

A single multipurpose room serves for dining, visiting and educational programs. A trailer jutting off the back of the original building has been added within the past year to relieve some of the congestion.

The sheriff is proposing to build a new jail on county-owned land at the airport.

In a six-page letter to Kathleen Dennehy, state acting commissioner of correction, obtained by the Globe, Mr. Thistle outlines the details of the attacks.

Mr. Thistle alleges that in June correctional officers T.J. Roginski and Michael Trance propositioned inmate Jason Labbe to attack Mr. Garcia in return for "chew," a container of chewing tobacco. He says they also promised to "make his time comfortable and get him some work details to lessen his sentence."

Mr. Thistle alleges the attack was intended to settle a score between Mr. Roginski and Mr. Garcia, who formerly employed Mr. Roginski's girlfriend and dismissed her over a financial dispute.

Mr. Roginski and Mr. Trance did not return phone calls from the Gazette.

Mr. Thistle wrote that after the assault he told officials at the jail that several officers had asked Mr. Labbe to beat up Mr. Garcia. Soon afterward Mr. Labbe was moved into the same cell as Mr. Thistle, a move he suggested was meant to intimidate him into quieting down about the incident.

Mr. Thistle said Mr. Labbe repeatedly threatened him, and then in September attacked him in an isolated area of the jail facility. Mr. Thistle suffered a broken nose and injured eye in the incident.

Sheriff McCormack said this week that his initial inquiries into Mr. Garcia's beating turned up no evidence of official wrongdoing.

"There started to be rumors about the possibility that an officer had been involved. We questioned the individual and put that to bed," Mr. McCormack said, adding that rumors among the inmates persisted over time.

Mr. McCormack said after Mr. Thistle was assaulted, "he started to come forward with circumstantial evidence that the inmate who assaulted him had some involvement with one or more officers with regard to the assault."

The sheriff then contacted the local state police, who conducted preliminary interviews. The investigation soon was turned over to the Cape and Islands district attorney's office, which is investigating the matter in conjunction with the Cape and Islands State Police Detectives Unit.

The officers under investigation remain on duty.

On March 4 the sheriff ordered Mr. Thistle's transfer to the South Bay House of Corrections in Boston to serve the remainder of his 18-month drug sentence.

Sheriff McCormack said he ordered the move both out of concern for the safety of Mr. Thistle and for the morale of the department.

"The [Globe] reporter started calling the jail, asking to talk to inmates and to staff. It was very disruptive, and I had several officers come to me upset."

Of Mr. Thistle, the sheriff said, "he continued on a daily basis to make allegations to officers and to other inmates, and I received information that he was colluding with other inmates for his personal gain. It seemed there was something else going on here, and it was nothing we wanted to be a part of."