Funes, who takes office in June, said he had sent his son Alejandro to France to protect him from violence in his own country, only for the young man to be killed at 27 years old, for no reason, by a drunk attacker on a Paris bridge.

"We had decided to move him from El Salvador because there are fewer opportunities than here. We thought he would be safer here because in our country it is a violent society with a high crime rate," Funes said in the witness box.

"I would never have imagined that he would be beaten to death here and that he would not have a chance to fulfil his dreams," said Funes, bursting into tears as he spoke.

Alejandro Funes, 27, was a photography student. He was killed in October 2007 on the Pont des Arts, near the Louvre museum, where he was enjoying music and conversation with a group of fellow Latin-American students.

The man standing trial for murder, Mohamed Amor, has confessed to the killing. He says he was drunk at the time and provoked the students to a fight for no particular reason. Alejandro Funes was killed by a blow to the head with a heavy object.

"I didn't mean to kill him. I'm sorry," a pale Amor told Alejandro's family during the hearing.

Mauricio Funes, 49, is a former TV journalist who hosted local news programmes critical of past governments. He won El Salvador's presidential election in March for a party of former Marxist guerrillas.

It was a momentous victory for the left in a nation where memories of the 1980-92 civil war that killed 75,000 people, many by right-wing death squads, hang heavy over politics.

Funes cried as he recalled in court that his son had called him the day before his death to congratulate him on being designated as the party's presidential candidate.

"We shared the same ideals, the same dreams for our lives, a desire to transform El Salvador, to make it a fairer society that would put an end to violence," Funes said.

The verdict will be handed down on Friday. Amor faces up to 30 years in jail.