Dozens of the people who were on the boat that sank near the Italian coast last month were raped and tortured in Libya before starting their journey, Italian police said.
The police revelation on Friday came after they announced the detention of Mouhamud Elmi Muhidin, a Somali citizen, who is believed to be the alleged organiser behind the smugglers' ship packed with migrants that sank off the coast of a southern Italian island, killing more than 365 migrants.
According to migrants' testimony, the 20 women in the group were repeatedly raped and offered to Libyan visitors "as if they were a cup of tea".
Muhidin, Libyan militiamen and Sudanese traffickers all took part in the alleged assaults in a detention centre in Sabha in southwest Libya, that Italian prosecutor Maurizio Scalia likened to "a concentration camp".
"They forced us to watch our men being tortured with various methods including batons, electric shocks to the feet. Whoever rebelled was tied up," read the testimony of a 17-year-old Eritrean girl in the investigation, Italian newspaper La Repubblica daily reported.
The migrants were forced to pay up to $3500 for their freedom and their onward journey to the Libyan coast and a boat to Italy.
"The women who could not pay were assaulted," the girl was quoted as saying in her criminal charge.
She also described in horrific detail her own sexual assault, saying that Muhidin was one of the three men who raped her.
"They threw me on the ground, held down my arms and covered my mouth, and poured gasoline on my head, which burned my scalp, skin and eyes," she said through a translator. "And then, not yet happy, the three took turns raping me."
Lynched by his victims
Muhidin, who was identified by survivors, was attacked and nearly lynched by his victims in the immigrant centre on Lampedusa when he arrived there on October 25 after making the boat crossing from Libya himself, setting into motion the police investigation, the warrant said.
The police said they had not yet worked out why Muhidin had come to Italy but added that he "may have been looking for criminal contacts".
"He was one of the leaders of the trafficking organisation," a police spokeswoman told AFP news agency.
Muhidin faces charges of kidnapping, sexual assault, people trafficking and criminal association with the goal of aiding illegal immigration.
If convicted, Muhidin faces a maximum prison sentence of 30 years.
He was flown to the Sicilian capital Palermo on Thursday from the southern island of Lampedusa. The Palermo court announced his arrest on Friday. He has not yet spoken to a lawyer, been questioned by prosecutors, or entered a plea, investigators said.
Migrants from Eritrea and Somalia frequently speak of abuses along their journeys to Europe, particularly in an increasingly lawless Libya following the fall of dictator Moamer Kadhafi.
Their allegations are rarely investigated, however, and migrant rights groups complain that more international action should be taken to ease their plight in the countries they transit through.
Libya is the departure point for two thirds of the boats that set out for Italy from north Africa. Since the shipwreck, Italy has stepped up navy patrols and is using drones to search for boats making the dangerous crossing.
Italian authorities have vowed to crack down on the people trafficking rings that have been behind the influx of more than 35,000 asylum-seekers so far this year to the country's coasts.
Most of them come from Eritrea, Somalia and Syria and Italy has asked for the European Union to step up assistance in dealing with the arrivals and countering the criminal networks behind them.