A Syrian national was charged and jailed on Sunday as part of an inquiry into a shipwreck in the English Channel last week that claimed the life of a migrant, prosecutors said.
The man from Syrian Kurdistan, born in 1993, was charged with manslaughter, unintentional injury, deliberate endangerment and aiding illegal entry and residence, said Saint-Omer public prosecutor Mehdi Benbouzid.
He is suspected of having piloted a boat carrying around 60 migrants, including children, a charge he denies.
A second man suspected of also piloting the boat is still being sought.
The boat left Oye-Plage, east of Calais, on Thursday night and capsized off the nearby commune of Gravelines.
One man died and two other passengers are missing, according to the regional maritime authority.
In a separate incident, the body of another migrant was found on the beach at Sangatte on Friday after a failed Channel crossing attempt.
A boat carrying around 70 people had gone to sea before returning "following engine damage", according to the public prosecutor's office.
Around 40 other migrants who intended to join the group had remained on the beach at Sangatte.
Police were present on the beach and intervened, and a 33-year-old Iraqi man was in police custody on Sunday as part of the inquiry, according to regional prosecutors.
"The suspect appears to have been involved in the crossing scene, but also incited a number of migrants to attack the police when the boat returned," prosecutors said.
The cause of the victim's death had yet to be determined.
On Friday alone, 292 migrants reached the UK after crossing the Channel in seven boats, according to the UK Home Office's count. On Saturday, 55 migrants reached the UK in a single boat.
As of late November, more than 28,000 people have crossed the Channel since the start of this year, according to British government statistics, compared with almost 46,000 over the whole of last year.