The family of murdered British aid worker Margaret Hassan spoke of their anger last night after a man was jailed in connection with her killing.

Mustafa Mohammed Salman al-Jabouri was jailed for life for aiding and abetting the kidnappers of the Care International worker.

Mrs Hassan's family said it was "devastated and appalled" that the defendant could be released within months after the court decided he had not been involved in the murder.

Mrs Hassan, 59, was taken hostage in October 2004 and killed just under a month later, but her body has never been found.

The Dublin-born charity worker had British, Irish and Iraqi nationality and had lived in Iraq for 30 years.

The three men were arrested by US troops in May last year.

Muhssin Ahmed, aged 39, a guard at a mosque that figured in the case, and Qassim Muhammad, aged 33, who attended the mosque, were found innocent of helping the kidnappers.

Salman denied any links with the kidnappers.

He told the judge that he took a plastic bag from the sheik of a mosque south east of Baghdad that he used to attend, but he did not open the bag for two months.

"I opened the plastic bag to find ... the credentials of Margaret Hassan," he said.

He said he returned to the sheik, who promised to take the bag later, but disappeared. He said security forces raided his house and found the bag.

Mrs Hassan, who was married to an Iraqi, was one of the highest-profile figures to fall victim to the wave of kidnappings sweeping Iraq. In a statement, Mrs Hassan's family said they were struggling to understand the decision of the court, reached after a brief hearing.

The statement said: " Mustapha Al-Jabouri was found guilty of 'joining the group who kidnapped Margaret'.

"This man was found with Margaret's personal belongings. He had used her mobile telephone up until the eve of her death, to make demands of her husband Tahseen.

"He admitted to the Iraqi police that he had interrogated Margaret. Why was he not found guilty of murder?"

The remaining two defendants, they said, had showed "neither pity nor humanity".

Deirdre, Geraldine, Kathryn and Michael Fitzsimons said: "Justice has not been done." They added: "They did not have the decency to return her body to her family to allow us to bury her with the dignity she deserves."

Relatives of Mrs Hassan - a Roman Catholic, who had dual Iraqi and British citizenship - again criticised the British authorities for their handling of her kidnap, calling it "inept".

"Their refusal to interview the kidnappers who were arrested by US forces on May 1 2005 leaves our family to draw one conclusion: they would have to admit to incompetence in this investigation.

"We feel that Margaret has been betrayed and that truth and justice have been denied.

"Today's judgment gives a green light to all kidnappers and murderers in Iraq to continue their terrible deeds. Both the British and Iraqi governments should hang their head in shame.

"Margaret's loss is not only to her family but also to the Iraqi people for whom she worked tirelessly and for whom she gave her life."