By Sui-Lee Wee

BEIJING (Reuters) - Six Chinese Communist Party officials have been sentenced to between four and 14 years in jail for torturing another official to death, lawyers and his ex-wife said on Monday, in a case that shed light on the workings of the party's judicial system.

The sentences marked a rare instance of legal punishment handed down over the abuse of a party official detained under the organization's secretive extra-legal detention process, lawyers for the family of the dead man said.

A court in the eastern city of Quzhou issued the verdicts on September 30, a decision not reported by Chinese media. The trial had opened on September 17.

The six officials were convicted of intentional infliction of harm leading to death over the drowning in April of Yu Qiyi, 42, a chief engineer for a state-owned investment firm in the nearby city of Wenzhou. Yu had been dunked repeatedly in a bucket of ice-cold water.

It is not precisely clear why Yu was being investigated, although it was possibly related to a land deal, according to his family's lawyers.

Yu had spent 38 days under "shuanggui", a form of detention imposed on party officials being investigated for disciplinary violations.

Five officials from the party's corruption watchdog, the Central Commission for Discipline Inspection, were given sentences of four to 14 years, according to a lawyer for one of the accused and lawyers representing Yu's family. The five were Zhang Fangchao, Li Xiang, Cheng Wenjie, Wu Zhiwei and Nan Yu.

Gu Chenfu, from the local prosecutor's office, was sentenced to eight years. The six had faced a maximum penalty of death.

"In reality, they want to control the scope of people who can be targeted for this," said Pu Zhiqiang, a lawyer for Yu's family, referring to the trial.

"But the fact that members of the Central Commission for Discipline Inspection can face these kinds of criminal penalties, this is already rare."

"Shuanggui" refers to the time and place at which party members summoned by the commission must appear for questioning. Family members are often kept in the dark and detentions can last for an indefinite period.

Two other Communist Party officials died while under "shuanggui" between April and June this year, according to lawyers involved in those cases.

ACTING ON ORDERS - LAWYER FOR ONE OF THE ACCUSED

Chi Susheng, a lawyer for Li Xiang, called her client's jail term of 10 years unreasonable, adding the accused had appealed.

All six men had testified that Yu was deprived of sleep and beaten during his extra-judicial detention, according to a defense statement by Chi, who cited testimony from the accused. Her statement was seen by Reuters.

But they insisted they had treated Yu harshly at the behest of more senior officials in the commission, according to the statement.

"The higher-up officials have not been held accountable, don't you think this is unfair?" Yu's ex-wife, Wu Qian, told Reuters by telephone from Wenzhou. "We are very dissatisfied that the main culprits have not been brought to justice."

Pu said the party was making the six officials scapegoats.

Reuters was not immediately able to locate lawyers for the other five jailed officials. Neither the government nor the party has publicly given an account of what happened. The trial has not received any coverage in state-run media.

An official from the Quzhou court, who declined to be identified, told Reuters she was aware of the case but declined to confirm the sentences.

During the two-day closed-door trial, lawyers representing Yu's family were thrown out of court.

Investigators put Yu's head in a bucket of ice-cold water and held it down repeatedly, eventually causing his death, according to lawyers for his family. Yu was also beaten and his body scarred by what appeared to be cigarette butt marks.

The verdicts come as China wages war on corruption.

President Xi Jinping has pledged to go after "tigers" and "flies" in the battle against graft, referring to both political heavyweights and low-ranked officials.

Ousted Chinese politician Bo Xilai, who was sentenced to life imprisonment on charges of corruption and abuse of power last month, was subjected to "shuanggui" for 17 months.

During his trial, Bo recanted an earlier confession to party investigators saying it was made under psychological pressure.

Pu said it was unlikely that officials would do away with "shuanggui" as a tool to fight corruption, but Yu's case might prompt them to rethink the brutality of the system.

"The lesson that should be learned from this case is that if you wantonly beat a person to death, your organization will not stand up to fight for you," he said.

(Additional reporting by Beijing Newsroom. Editing by Dean Yates)