Retired army general Humberto Gordon has been linked to the killing of influential trade union leader Tucapel Jimenez 17 years ago.

Mr Jimenez, a leading critic of General Pinochet, was found shot in the head with his throat cut.

He was reportedly organising one of the first major protests against the Pinochet regime when he was killed.

Mr Jimenez, considered Chile's most influential union boss at the time, headed the now dissolved National Information Centre (CNI) between 1980 and 1986.

Correspondents say his unsolved murder has remained a cause celebre for human rights activists, who accuse the intelligence service of involvement in hundreds of killings and disappearances during the military era.

Pinochet 'laments' violence

General Pinochet, who is under house arrest in England, has meanwhile issued a letter expressing sorrow for the deaths which occurred while he was head of state.

The President of the Chilean Senate with Gen Pinochet's letter

But he stopped short of the apology demanded by his opponents, who dismissed the letter as a publicity stunt.

This month sees the start of extradition proceedings against the 83-year-old general which could result in him being sent to Spain to stand trial for human rights abuses.

The general's six-page letter was sent to the Chilean Senate of which he is a life member.

"The pain of those who suffered was not alien to me in the past, nor now," he wrote. "I lament all the situations of belligerence and acts of violence that caused them."

But Mr Pinochet's opponents say the letter is an attempt to gain public sympathy in the run-up to his extradition hearings.

The general's supporters, who make up a powerful minority in Chile, are hoping he may be released on grounds of compassion, due to ill health.

Doctors say a series of medical check-ups in recent weeks show a general decline in his well-being.