A lorry driver was told to give migrants “air quickly” but not to let them out during a 12-hour journey where they suffocated to death, a court has heard.
Lorry driver Maurice Robinson, received a message from his boss to give the Vietnamese nationals, sealed inside the pitch-black refrigerated unit “air quickly, but don't let them out", jurors were told.
With no signal in the container that had risen to a temperature of 38.5C, one of the victims - a 28-year-old woman - wrote a text message that was never sent, saying: "Maybe going to die in the container, can't breathe any more dear."
Lorry driver Eamonn Harrison and Gheorghe Nica are on trial at the Old Bailey accused of the manslaughter of the 39 migrants who were found dead after the lorry arrived in Purfleet, Essex, in October last year.
The pair are also accused of being part of a people-smuggling conspiracy with another lorry driver, Christopher Kennedy, and Valentin Calota.
Opening their Old Bailey trial, Bill Emlyn Jones said the people-smuggling team had operated successful runs before the one in October last year that went "dreadfully wrong".
He told jurors: "Obviously, any time you fill an airtight container with a large number of people, where they will be left for hours and hours, with no means of escape and no means of communication with the outside world - well, it is fraught with danger."
Jurors were told the cost of being smuggled across the English Channel in the back of a lorry was some £10,000 per person.
On October 22 2019, 39 Vietnamese nationals - men and women, aged between 15 and 44, - were loaded into the back of a lorry in northern Europe, he said.
Harrison drove them to Zeebrugge in Belgium, and unhooked his trailer where it was loaded onto a cargo ship bound for Purfleet, in Essex, jurors heard.
Maurice Robinson, then collected the trailer from Purfleet when it arrived just after midnight on October 23.
Mr Emlyn Jones said that by then it had been some 12 hours at least since "any meaningful amount of fresh air had been let into the sealed container".
The prosecutor said: "Robinson drove out of Purfleet port and almost immediately stopped and opened the doors at the back.
"What he found must haunt him still. For the 39 men and women inside, that lorry had become their tomb."
When Kennedy learned of the deaths, he told a friend it "must have been too many and run out of air", the court heard.
Nica was said by the prosecution to be a "key player" in the smuggling operation.
On October 23 last year, he was in the area of Purfleet "primed" to meet the human cargo and was the second person Robinson called within seconds of the discovery of the bodies, jurors heard.
Nica, 43, of Basildon, Essex, and Harrison, 23, of Mayobridge, Co Down, Northern Ireland, deny 39 counts of manslaughter.
Nica has admitted conspiracy to assist unlawful immigration between May 1 2018 and October 24 2019.
Harrison, Calota, 37, of Birmingham, and Kennedy, 24, of Co Armagh, Northern Ireland, deny the conspiracy charge.
The court heard Robinson and haulage boss Ronan Hughes had pleaded guilty to the manslaughters and the people-smuggling plot.
Two other defendants have also admitted their part in the wider people-smuggling operation.
The trial before Mr Justice Sweeney is expected to go on for up to six weeks.