US vice-presidential candidate Sarah Palin faces possible censure today with the conclusion of an investigation into allegations that she committed a serious abuse of power by sacking the head of the Alaskan police force when he refused to become involved in a family feud.

Republicans last night failed in suppressing the report after Alaska's supreme court refused to shut down the investigation. Palin is expected to be criticised for failing to cooperate with the inquiry into the Troopergate affair, so called because she is alleged to have dismissed the state's public safety commissioner, Walt Monegan, after he refused to sack her former brother-in-law, a state trooper. It is unclear whether the investigation will find that Palin, the governor of Alaska, is guilty of firing Monegan because he refused to move against the trooper, Mike Wooten, or whether it will accept her argument that she had other reasons to dismiss him.

Palin's husband, Todd, attempted to shoulder much of the blame for the pressure Monegan faced after refusing to fire Wooten; in a statement to the investigation on Wednesday he said: "I make no apologies for wanting to protect my family and wanting to publicise the injustice of a violent trooper keeping his badge."

He said he had never instructed Monegan to sack Wooten, but his statement, made public by his lawyer, conceded: "We had a lot of conversations about a guy who threatened my family and verbally assaulted my daughter." His wife, he said, had finally told him to "drop it".

Stephen Branchflower, a former prosecutor who is conducting the investigation on behalf of the Alaskan state legislature, is known to have examined emails from Mrs Palin to Monegan, including one complaining that "this trooper is still out on the street, in fact he's been promoted".

Some Palin aides are also expected to face censure. They appear to have been unaware that Monegan's Department of Public Safety (DPS) routinely recorded incoming telephone calls, with the result that Branchflower was able to obtain recordings of a number of conversations.

He is also thought to have obtained details of emails sent between Palin, her husband and a number of senior officials in her administration.

The investigation has focused on events leading up to Monegan's sacking last July. Wooten and the governor's younger sister, Molly McCann, had been through an acrimonious divorce and child custody dispute, during which members of Palin's family had accused him of a range of crimes and disciplinary offences. In March 2006 Wooten was found guilty of a number of offences, including threatening behaviour and shooting his stepson with a Taser stun-gun on a low power setting. He was briefly suspended and given a final written warning, but after Palin came into office nine months later, her aides are alleged to have repeatedly urged Monegan to reopen the case. Monegan says his refusal to do so cost him his job.

Branchflower will present his conclusions today at a meeting of Alaskan state senators and representatives.