A woman saw nine people get into a lorry in northern France the day before 39 Vietnamese migrants were found dead inside it in the UK, a court heard.
The witness, who said police were alerted, said the group were dropped by taxi near a farm shed before the white lorry stopped and they got in.
A little later on 22 October 2019, a lone man arrived saying he was "looking for his friends", the Old Bailey heard.
Four men are on trial after the migrants' bodies were found in Essex.
Jurors have heard the 39 victims, aged between 15 and 44, had suffocated in the sealed trailer - which was found on an industrial estate in Purfleet - as the temperature inside reached 38.5C.
Gheorghe Nica, 43, of Basildon, Essex, and lorry driver Eamonn Harrison, 23, deny the manslaughters of 39 Vietnamese people, aged between 15 and 44.
Mr Harrison, of Mayobridge, County Down, Christopher Kennedy, 24, of County Armagh, and Valentin Calota, 37, of Birmingham, deny being part of a people-smuggling conspiracy, which Mr Nica has admitted.
'Looking for friends'
A statement from carer Laetitia Mockelyn was read to the trial, in which she said she had heard Estelle Duyke call the Gendarmes on 22 October about migrants being seen close to her elderly mother-in-law's house, in Bierne.
She said she later saw the lone man being dropped off by a taxi after the lorry had left with the nine people who had arrived earlier.
When he was approached the man said in English he was "looking for his friends", before walking off in the direction of a factory.
When the Gendarmerie arrived they checked the shed where the nine people had waited but "there was no-one there", Ms Mockelyn said.
She said the nine all appeared to be aged under 35 and among them was a woman wearing a padded jacket, white woolly hat and small backpack, and a "slightly-built" man in jeans and classic black cap.
The man who arrived after the lorry departed was described as being of small build and wearing blue jeans, a padded jacket and Adidas backpack.
Ms Mockelyn told officers she had never seen anything like it before.
Lorry driver Eamonn Harrison, 23, allegedly picked up the migrants in his trailer before dropping it at the port of Zeebrugge in Belgium, on 22 October.
The court heard the temperature inside the trailer had already risen from 11.7C to 15.6C by 10:30 BST.
The next morning the trailer was collected by Maurice Robinson in Purfleet, Essex, and he discovered the bodies of the men, women and children, the jury was told.
Prosecutors said Harrison had two encounters with the police in the days before he allegedly collected the migrants. The first time was due to the fact he was intoxicated and the second because his trailer was parked illegally.
Meanwhile, haulage boss Ronan Hughes, Robinson and alleged key organiser Gheorghe Nica were caught on CCTV at the Ibis Hotel in Thurrock, Essex, on the evening of 18 October.
Hughes, 41, and Robinson, 26, have pleaded guilty to 39 counts of manslaughter.
The trial continues.