Two brothers charged with the car-bomb assassination of the Maltese journalist Daphne Caruana Galizia have both been sentenced to 40 years in prison, after dramatically pleading guilty to her murder on the first day of their trial.

Caruana Galizia, who had investigated political corruption in the European Union’s smallest member state, died in an explosion that destroyed her car as she drove away from home on 16 October 2017.

George Degiorgio, 59, and Alfred Degiorgio, 57, were given 40-year prison terms, meaning three of the seven men so far accused of conspiring to commit the murder have now been convicted.

The trial in Valletta’s central court, which has drawn international attention, began on Friday morning with both men denying all six charges laid against them, including wilful homicide, causing a fatal explosion, illegally possessing explosives and criminal conspiracy.

In an unexpected twist, after an extended midday break that followed a morning during which the prosecution set out its case, the brothers were ushered into the courtroom and asked to re-enter their pleas, the Times of Malta reported.

Mandy Mallia lights candles at a memorial to her sister Daphne Caruana Galizia in Valletta on Friday. Photograph: AP

George Degiorgio stood before the judge, who asked him again: “How do you plead?”

In front of Caruana Galizia’s three sons and her husband, he replied: “Guilty.”

Alfred Degiorgio, who uses a wheelchair and is under medical supervision after going on hunger strike to protest against the prosecution, entered the same plea.

The judge told the court the two men had been examined by a doctor and a psychiatrist beforehand, to verify they were of sound mind and understood the implications of changing their legal position.

In proceedings that were being monitored by an array of international observers, with members from press and free speech groups including Reporters without Borders, the Committee to Protect Journalists and Article 19 seated on the benches, the brothers were each sentenced to four decades, although time served is likely to be reduced if they can show good behaviour.

Their accomplice Vincent Muscat, a member of the gang that planted the bomb, avoided a trial after earlier changing his plea to guilty and providing evidence for the prosecution. Muscat is serving a 15-year sentence.

Daphne’s son Paul Caruana Galizia was the first family member to respond publicly. He tweeted: “A break in the clouds.”

A break in the clouds.

Guilty: Degiorgio brothers admit killing Daphne in sensational turnaround https://t.co/uIrRkbkWd0

— Paul Caruana Galizia (@pcaruanagalizia) October 14, 2022

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During a series of heated exchanges, George Degiorgio asked to address his victim’s family but was reportedly shouted down and left the courtroom. His brother then rose from his wheelchair and spoke to Caruana Galizia’s widower, telling him: “Now you will know the whole truth, whoever was involved either way.”

The brothers had unsuccessfully tried to negotiate a pardon in exchange for naming bigger alleged conspirators, including a former minister whose identity has not been revealed.

Prosecutors alleged they were hired to carry out a contract killing, paid for by a top Maltese businessman with government ties. That businessman, Yorgen Fenech, has been charged and will be tried separately.

Fenech was indicted in 2019 for alleged complicity in the killing, by either ordering or instigating the commission of the crime, inciting another to commit the crime or by promising to give a reward after the fact. He was also indicted for conspiracy to commit murder. Fenech has entered not guilty pleas to all charges. No date has been set for his trial.

A self-confessed middleman, the taxi driver Melvin Theuma, was granted a presidential pardon in 2019 in exchange for testimony against Fenech and the other alleged plotters. Two men, Jamie Vella and Robert Agius, have been charged with supplying the bomb, but their trial has not yet begun.

The case had taken years to reach trial, delayed by attempts from the defendants to have proceedings dismissed. They had requested presidential pardons, filed constitutional objections and objected on fair trial grounds. They had complained of being unable to find their own counsel and protested about having to rely on legal aid lawyers, saying it was a breach of their rights.

A well-known newspaper columnist and magazine publisher, Caruana Galizia, 53, had also made a name as Malta’s foremost investigative journalist, publishing her findings on her website, Running Commentary. She reported extensively on suspected corruption in political and business circles in the Mediterranean island nation, an attractive financial haven.

Among her targets were senior members of the government of the then prime minister, Joseph Muscat, whom she accused of having set up offshore companies in tax havens days after entering office. But she also targeted the opposition. When she was killed she had become a target for online and political attacks, was facing more than 40 libel suits and her bank accounts had been frozen.

The bomb had been placed under the driver’s seat and the explosion was powerful enough to send the car off the road and into a field.

The 2019 arrest of Fenech, the heir to a property empire with connections to senior government officials, prompted a series of mass protests in the country, eventually forcing Muscat to resign.

The European parliament president, Roberta Metsola, a Maltese politician who has supported the Caruana Galizia family’s long struggle to secure prosecutions and political reforms, said the fight must continue. “This is not justice,” she said. “Now for those who ordered and paid for it, those who protected them and those who spent years doing everything imaginable to try to cover it up.”