British police have arrested another man in connection with the deaths of 39 Vietnamese nationals whose bodies were discovered in the back of a refrigerated truck near London last month.

A 23-year-old unnamed man from Northern Ireland was apprehended early Friday morning on a highway in the town of Beaconsfield, some 25 miles northwest of London. He was arrested on suspicion of conspiracy to traffic people and conspiracy to assist unlawful immigration. He remains in custody, according to Essex police.

It’s the latest arrest in the ongoing investigation into the 39 people who were found dead on Oct. 23 in a tractor-trailer at an industrial park in the town of Grays in Essex, about 20 miles east of London.

Essex police initially believed the victims were Chinese, but further investigation revealed that they were from Vietnam and are suspected to have paid smugglers to get them into the United Kingdom.

Earlier this month, Essex police released the identities of all the victims, 31 males and eight females, who ranged in age from 15 to 44.

The cause of their deaths death has yet to be determined, although one victim’s family reported receiving text messages from their daughter saying she couldn’t breathe.

The driver of the truck, 25-year-old Maurice Robinson, also of Northern Ireland, has been charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration as well as money laundering. He is next scheduled to appear in court on Nov. 25.

Authorities in the United Kingdom have asked for the public’s help in locating two brothers from Northern Ireland — 40-year-old Ronan Hughes and 34-year-old Christopher Hughes — who are both wanted on suspicion of manslaughter and human trafficking in connection with the case in Essex.

Meanwhile, Essex police are also seeking the extradition of another Northern Irish man, who appeared in court in Dublin earlier this month and was remanded in custody. Eamonn Harrison, 22, has been charged with 39 counts of manslaughter, as well as human trafficking and immigration offences in connection with the case in Essex. The extradition proceedings to bring Harrison to England are pending, and he is expected to next appear in court in December.

Three other suspects — two men and a woman — were arrested in late October and questioned on suspicion of manslaughter and conspiracy to traffic people, but they have not been charged and were released on bail, according to Essex police.