Marie Andrews and her partner Stewart Cox allegedly spotted a migrant drop outside their mobile home in Orsett, Essex, early on October 11th last year.
Prosecutors claim it was one of two successful people-smuggling runs before 39 Vietnamese nationals suffocated in a trailer en route from Zeebrugge to Purfleet on October 23rd last year.
Giving evidence at the Old Bailey in London on Monday, Ms Andrews told how she dialled 999 on October 11th, after landscaper Mr Cox left for work and found a lorry and four cars in their lane.
She told the operator that “a load of immigrants just got out of a lorry into Mercs”.
Ms Andrews told jurors there were about 15 migrants.
She said: “I saw some legs come out. It was a shock, like anybody would be shocked to see this, particularly down a lane people would not know.
“I was on the phone, I’m standing there looking out as I’m speaking on the phone.
“I didn’t take my eyes off the lorry while I was on the call.”
Ms Andrews went on to call the non-emergency number 101 twice, the court heard.
In the calls, she linked one of the Mercedes cars she had seen to an earlier incident on October 4th.
On that occasion, she told police that “the same guy who is obviously running this was having an argument and having some guy by the throat”.
The witness also told jurors that on October 18th, she saw a red lorry in the lane, but did not see any migrants.
'Dodgy stuff'
Under cross-examination, Ms Andrews alleged there was “dodgy stuff” going on in the area.
But she added that the sighting on October 11th was the first time she had been aware of migrant issues.
Alleged key organiser Gheorghe Nica (43) of Basildon, Essex, and lorry driver Eamonn Harrison (23) deny the manslaughters of 39 Vietnamese people, aged between 15 and 44.
In her statement read to court, Ms Andrews described ringing 101 again after seeing the news of the 39 migrant deaths on social media.
She said: “I immediately recognised this cab and trailer on the news as certainly being the same one that I had seen on both October 11th and October 18th, 2019.”
As a result of that call, Ms Andrews became a witness in the trial.
Harrison, of Mayobridge, Co Down, Christopher Kennedy (24), of Co Armagh, and Valentin Calota (37), of Birmingham, deny being part of a people-smuggling conspiracy, which Nica has admitted.
Jurors have heard that four others have admitted a role in the people-smuggling ring.
