Police arrested a Syrian in Germany on Wednesday suspected of helping to set a freighter packed with migrants on a collision course with the Italian coastline.

Italian and German forces, working in collaboration, handcuffed the 26-year-old alleged trafficker in Soest in the country's northwest and were hunting for his brother, 22, also believed to have played a role in the major maritime drama.

The brothers, plus a third accomplice, were suspected of having helped set the Moldovan-registered Blue Sky M freighter on course for Italy in December before abandoning the controls, locking the engine on and hiding themselves among the 768 asylum seekers on board.

Italy's coastguard managed to board, unlock the engine and bring the vessel under control just five miles (eight kilometres) from the cliffs.

An eight-month investigation found the Blue Sky M voyage was organised by an international network of criminals operating between Lebanon, Romania, Syria and Turkey, police said in a statement.

And text messages found on the phone of the Syrian captain -- who was arrested on arrival in Italy after migrants identified him -- showed how the passengers, who had paid up to 6,000 euros ($6,690) for a place onboard, were treated like livestock.

"We're on our way to Mersin (in Turkey) to pick up sheep," one message said, according to police, who did not give details of who sent or received the texts.

Another read: "I'm organising the transfer of 30 sheep at the cost of 4,000 euros each".

"Tell those sons of bitches to stop complaining," read a third message, while migrants later said they had endured a hellish journey packed like cattle in the hold, where most were cold, wet, miserably sea-sick and fearful for their lives.