MELILLI, Sicily — Body No. 421, bagged in midnight blue, is heaved from a refrigerated truck onto a metal stretcher and wheeled into the tent that serves as a morgue. It joins other putrefying corpses that fill the air with a pungent scent that clings to the clothing and hair of the living.

The body is that of a young man, one of hundreds who drowned 77 nautical miles off the coast of Libya in the deadliest known migrant disaster. Eighteen months later, volunteers are trying to find out who he was.

A volunteer reaches into the body bag and pulls out the dark, slime-covered remains. Another uses a sharp, black-handled knife to cut out samples for further study. Others examine the muscles and bone structure, photograph the skull and teeth and take notes on a clipboard.

The team’s leader, University of Milan forensic pathologist Cristina Cattaneo, emerges with a slimy pair of children’s jeans reading “Manchester United.” She hoses them down carefully. The jeans, and the personal effects found in the pockets, are among the most useful of clues.

It is the first time that forensic scientists have tried to build a full accounting of victims in a migrant disaster.

It was early evening on April 18, 2015, when the distress call came. A fishing boat packed with hundreds of people was in trouble, the caller said. The Italian Coast Guard radioed a nearby freighter and told it to provide assistance.

When they saw the approaching ship, the frantic migrants rushed to one side of the deck, causing the boat to list and then capsize. The boat sank to the bottom.

Twenty-eight people made it to safety. Hundreds more were locked below deck.

A year later, the Italian Navy returned to the site and used a complicated pulley system to bring the wreck to the surface. As the boat emerged from the water, the horror of what had lain below became clear.

“Water started coming out of various openings that the boat had on the side, we also saw human remains coming out of these openings,” said Rear Adm. Paolo Pezzutti, who was in charge of the operation. “It was a spectral vision we saw coming out of the water.”

Italian Prime Minister Matteo Renzi on Friday called for the ship to be placed in the European Union headquarters “to remind us how to fight selfishness.”

Back at port in Sicily, firefighters in protective suits, rubber gloves, goggles and helmets cut into the rusted hull with hatchets and saws.

They found bodies packed in almost unimaginably close quarters. There were five bodies for every square meter. Two hundred were locked in the engine room alone.

Meticulously, the firefighters filled 458 body bags. Many contained the remains of more than one person.

The team expects to complete the autopsies this month. Cattaneo predicts the volunteers will analyze some 700 bodies, maybe as many as 800 or 900. So far, all of the victims have been men and boys, mostly between the ages of 12 and 27.

When they are finished with their examination, the volunteers zip the bag back up and load body No. 421 into a metal container that will go inside a wooden coffin.

Using a black marker, Cattaneo carefully writes PM3900421 on the container — PM for “post mortem” and 39 for Italy’s telephone country code.

That’s the code that will mark the grave until the body is connected to a name.

European rules require that asylum-seekers register in the first country they enter. Because few of them want to end up in Italy, many leave their IDs back home.

That means Cattaneo’s team must rely on DNA samples from the bones, teeth, and the objects found on the bodies.

At Cattaneo’s Labanof laboratory in Milan, plastic baggies and small cardboard boxes containing items found in the migrants’ clothing sit in neat lines along the table. Cattaneo goes over them one by one.

Some contain ID cards that were sewn into clothing. Several bags contain little wooden sticks used for cleaning teeth. One has a photo of a saint.

Another contains what looks like a small brown candy in a pink wrapper. On closer inspection it’s a spoonful of dirt, bagged by the traveler as a memory of home.

The tragedy has done little to slow the business of trafficking in human lives. Smugglers in Libya continue to reap a fortune by taking migrants’ cash and piling them on top of one another in rickety vessels unfit to cross the Mediterranean.

So far in 2016, more than 316,899 people have reached Europe by sea, according to the International Organization for Migration.

Another 3,611 set out but never made it.

In December, the second stage of the process will begin: contacting relatives of those who had IDs on them, and searching for others who are looking for missing kin.

That won’t be easy. The dead came from Somalia, Eritrea, Ethiopia, Guinea, Sudan, Senegal, Mali, the Ivory Coast and Bangladesh, among other places. Some of those countries have repressive governments; others have poor populations with little access to internet or phones.

Cattaneo is working with Italy’s office for Missing Persons, run by High Commissioner Vittorio Piscitelli. The office has built a database of information gained from the autopsies.

When families searching for their loved ones reach out, the information they give will be compared with the data on file. Gathering that information will be perhaps the biggest challenge. The Red Cross has signed up to help.

“If we don’t have people to show the data to, or any data to compare it with, we risk doing all this work in vain,” Piscitelli said.

Despite the challenges, Cattaneo is determined to carry on. In a plane or train crash involving European and American victims, she notes, forensic experts rush to the scene and identify all the bodies. That isn’t the case in migrant tragedies.

“These bodies become nobody’s business,” Cattaneo says. “This is the largest mass disaster in Europe after the Second World War and it is the largest humanitarian crisis in terms of dead, unidentified bodies… but nothing has been happening for these people.”

Body No. 421’s final destination is a cemetery in Catania, on the island of Sicily. In an unkempt field lined with mounds of dirt, small black plaques list the codes associated with the bodies buried below.

Someday, the volunteers hope, the young man’s relatives may be able to put a name to the number and come to find him.

His dream of a new life in Europe was dashed, but at least he would have the chance to go home.