A truck driver pleaded guilty to 39 counts of manslaughter Friday in the deaths of dozens of Vietnamese immigrants who were discovered in the back of a container truck last year in southeastern England.

BRITISH POLICE IDENTIFY 39 VIETNAMESE MIGRANTS FOUND DEAD INSIDE REFRIGERATED TRUCK LAST MONTH

Ronan Hughes, 40, of County Armagh in Northern Ireland, entered the pleas in Central London Criminal Court. The victims were found dead in the back of the truck parked in an industrial park in the English town of Grays on Oct. 23, 2019.

The incident is one of the worst cases of human smuggling ever discovered in Britain .

The victims, ranging in age from 15 to 44, were crammed into the truck in an effort by human traffickers to smuggle them into the country.

Hughes also pleaded guilty to conspiracy to assist unlawful immigration of non-European Union citizens between May 1, 2018 and Oct. 24, 2019.

Hughes appeared alongside Eamonn Harrison, 23, of County Down, Northern Ireland, who is alleged to have driven the truck's trailer to the Belgian port of Zeebrugge before it sailed to Purfleet in England.

Harrison pleaded not guilty to 39 counts of manslaughter and one count of conspiracy to assist unlawful immigration and will face trial Oct. 5 with three others.

Gazmir Nuzi, 42, of Tottenham in north London, who appeared via video-link, pleaded guilty to a single charge of assisting unlawful immigration on or before Oct. 11, 2019 and April 18, 2020.

The pleas were not the first in the tragic case.

Another driver, Maurice Robinson, 25, of Craigavon in Northern Ireland, pleaded guilty to 39 counts of manslaughter in April. Robinson discovered the bodies after transporting the container from Purfleet to Grays.

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In June, Alexandru-Ovidiu Hanga, 28, admitted to one count of conspiring to assist unlawful immigration.

Investigators say the truck's container -- which is registered in Bulgaria -- entered the U.K. via ferry after leaving Zeebrugge.

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The Associated Press contributed to this report.