(LONDON) — Police raided two sites in Northern Ireland and questioned a truck driver as officers investigate the death of 39 people found in a container at an industrial park in southeastern England.

The truck and the trailer with the people inside apparently took separate circuitous journeys before ending up on the grounds of the Waterglade Industrial Park in Grays, 25 miles (40 kilometers) east of London on the River Thames.

British police said they believe the container went from the port of Zeebrugge in Belgium to Purfleet, England, where it arrived early Wednesday.

A National Crime Agency assessment report on serious and organized crime last year said there was a “greater focus” on rising smuggler numbers in Belgium after the closure of the Dunkirk migrant camp in 2017.