Sarah Palin abused her powers when she pressurised Alaska's public safety commissioner to fire her former brother-in-law, an investigation by a committee from the Alaska state legislature has concluded. But the probe said her dismissal of Walt Monegan in July, weeks before she was tapped as Republican candidate John McCain's running mate, was not illegal.

Although she violated a state ethics law that prohibits state officials from using their office for personal gain, the committee concluded her dismissal of Monegan was carried out in accordance with her constitutional powers.

The Troopergate inquiry, by 10 Republicans, four Democrats and independent former prosecutor Stephen Branchflower, concluded that the pressure applied by the governor, her husband and her aides on the police commissioner to fire her former brother-in-law, Mike Wooten, constituted "improper pressure to advance a personal agenda."

In other words, Palin's firing of Monegan was legal but her attempts to pressure him to fire Wooten were not. The report concluded that Monegan's refusal to fire Wooten was probably a "contributory factor" in his dismissal.

The 253-page report, released late on Friday night, will provide fodder to both sides of the political divide. The McCain campaign has already claimed the investigation was biased and its conclusions are tainted. The Obama campaign says it is further evidence of the sort of backroom politics and personal vendettas that Palin publicly claims to abhor. Monegan said on Friday night that he felt vindicated.

An ethics violation is a violation of state law and could be taken up by the state legislature as a basis for censure or impeachment, but it is unlikely any further action will be taken over the coming weeks.

The McCain campaign will now have to spend time defending Palin and dismissing the report's findings. The conclusions may force Palin to blunt her attacks on Obama as an underhand politician skilled in backroom tactics.

The key factor that led the committee to its decision was the role of Sarah Palin's husband Todd in the crusade, which seems to have teetered on the obsessional. The investigation concluded she knowingly allowed Todd Palin to use the governor's office and its resources in the campaign to have Wooten fired.

In his 25 pages of testimony, Palin acknowledges that he spoke to hundreds of people, including 16 state employees. While he disputes that she fired Monegan because of his refusal to fire Wooten, Palin's husband says their relationship deteriorated after Monegan suggested she get an appropriate car seat for their nine-week-old son. There were also tensions over refusals to make the commissioner's plane available to Palin. In a flurry of publicity Palin had sold the governor's plane to a private contractor.

Before she was named as McCain's running mate, Palin said she welcomed the investigation and promised her full co-operation. After it emerged there were tapes of Troopergate conversations, she acknowledged that her staff and her husband contacted Monegan over two dozen times. But days after she joined the McCain ticket, she hired a lawyer to represent her, and Republicans dispatched a top lawyer to Alaska in a bid to delay proceedings until after the election,

A cursory reading of the case suggests Palin became involved in a bitter divorce that flared into a family feud. She and her husband hired a private investigator to track Wooten's movements, leading to a complaint that he killed a moose out of hunting season and rode a snowmobile while on sick leave after a work-related injury.

In her crusade to have him fired, Palin made 36 allegations against Wooten, including domestic violence, drinking on the job and abuse of his 10-year-old stepson, on whom he used a stun gun. Palin also claimed he threatened to kill her father and represented a threat to the First Family of Alaska, a claim the committee ruled out.

As a result of Palin's complaints, Wooten was suspended for five days from his job. But the vendetta continued and several of her aides phoned Wooten's supervisors seeking his dismissal. Monegan refused to budge and in July this year his contract was terminated.