Investigators were looking into the cause of one of Europe's worst road accidents when a coach carrying 48 people plunged off a highway viaduct near Naples on Sunday.
Prime Minister Enrico Letta joined the throng of mourners at the funeral in Pozzuoli, a southern Italian industrial town where most of the victims came from.
"My brother was killed, it has broken me," said Fabrizio, a local resident in his forties who looked exhausted after a night's vigil at his brother's side.
Relatives huddled around the flower-draped coffins laid out in a gym hall, bending down to pray and kiss photographs of their loved ones displayed on the lids.
Around a dozen people fainted during a funeral mass and were carried out on stretchers. Two women had fits and were removed screaming and thrashing.
"We feel terrible. We all know each other here. We are like brothers and sisters," said one tearful mourner, Franco, who lost a friend in the accident.
The names of the victims were read aloud before local Catholic bishop Gennaro Pascarella led the mass assisted by priests who comforted the relatives and gave communion.
"Magistrates will have to clarify the causes of the accident and others will have to ensure this never happens again," Pascarella said in his homily.
"Political and religious institutions should not leave our brothers alone," he said, before the coffins were raised to applause and carried away.
Prosecutors are considering possible manslaughter charges over Sunday's accident and have said several people are already under investigation.
Hundreds of relatives on Monday had to spend agonising hours identifying the bodies of the victims close to the scene of the crash before the coffins were carried off.
The coach had rammed several cars after failing to brake on a bend, smashing through a highway crash barrier and plunging 30 metres (100 feet) down a slope.
Some witnesses quoted by Italian media said the bus had been gaining speed and "losing pieces" up to a kilometre before the actual impact.
One survivor said she thought the bus had lost a wheel before the crash and that the driver had tried to brake by sliding along the guardrail.
Ten coach survivors were still being treated in hospital on Tuesday – several with serious injuries — along with nine others who were injured in the cars.
"We want to know what happened," said Annibale Spira, another mourner at the funeral.
"We have a right to know because it's not the first time there has been an accident in that place. We want to know why precautious were not taken," he said.
Letta spoke of an "enormous tragedy" for Italy and President Giorgio Napolitano called for "stronger engagement" to guarantee road safety in Italy.
Rosario Cantelmo, the prosecutor overseeing the investigation, said: "We will do everything we can and we will ensure everyone gets justice".
The group on the coach was returning from a pilgrimage to Pietrelcina in the Campania region, the birthplace of Padre Pio, an Italian priest canonised in 2002 and worshipped in the country's south.
Rescuers were quick to remove the shattered coach from the wooded area off the highway but passenger belongings streaked with blood – including shoes, books and a torn teddy bear – still lay on the ground.
The coach crash was the deadliest in western Europe in the last decade and the worst in Europe since an October 2010 accident in Ukraine when 45 people died.