The Vietnamese migrants suffocated as they were transported in a sealed container from Zeebrugge in Belgium to Purfleet in Essex on the night of October 22nd and 23rd last year.
Alleged “key player” Gheorghe Nica (43) and lorry driver Eamonn Harrison (23) have denied their manslaughters.
On Monday, lawyers outlined their defence cases before the trial was brought to a halt amid Covid-19 fears as the first witness became ill while giving evidence.
Adjourning the Old Bailey trial until Wednesday, Mr Justice Sweeney told jurors the witness was having a Covid test to be “extra sure”.
The prosecution has alleged Nica, of Basildon, Essex, organised a team of drivers to pick up the migrants in Essex.
Nica has admitted plotting to people smuggle but denies involvement in the tragic run.
His lawyer, Aftab Jafferjee QC, said the prosecution had claimed “greedy exploitation” led to the “appalling dreadful loss of 39 human beings”.
If so, jurors should consider who knew that so many people were being transported that night, he said.
Mr Jafferjee pointed out the same number of vehicles, a panel van and two saloon cars, were deployed on October 23rd as on previous occasions.
He also questioned the roles of haulage boss Ronan Hughes and two outstanding suspects, including the “presence of the elusive and, we say, sinister Marius Draghici”.
The lawyer invited jurors to look at whether Nica was more of a “gofer” for Hughes.
He said: “One of the issues is whether Nica was an organiser, as the prosecution suggest, or an occasional participant as and when required.
“In order to determine the issue you will need to consider the reason why he was in the country at all organising things or simply whether he was waiting for his and his family’s passports to arrive from the Home Office.”
Mr Jafferjee suggested Nica had a “peripatetic lifestyle” living “sofa to sofa” working at various lorry yards and garages.
He also alleged that the farm used as a pick-up point was involved in a “range of lucrative illegal activities”.
He told jurors: “You understand straight away why that is important because it goes to the issue whether my client on the 22nd/23rd was involved in migrant smuggling or anything else.”
The Old Bailey has heard Harrison, of Mayobridge, Co Down, dropped off the trailer containing human cargo at Zeebrugge on October 22nd but denied knowing they were there.
His lawyer, Alistair Williamson QC, told jurors: “Much of the Crown’s case is agreed. The question is what is the correct interpretation of that evidence.
“The two issues which we ask you to focus on during the Crown’s case are one: what is Harrison shown to know about his load so that you are sure?
“And two: who was with him in the cab of his vehicle on various dates in October and what role did that person play?”
Harrison and co-defendants Christopher Kennedy (24) of Co Armagh, and Valentin Calota (37) of Birmingham, England, deny being part of the people-smuggling conspiracy.
The court has previously heard that four other defendants have already admitted their part in the plot.
Lorry driver Maurice Robinson (26) of Craigavon, Co Armagh, who found the 39 migrants dead in the container after picking it up in Purfleet, and Hughes (41) of Co Armagh, have admitted manslaughter.
