Dirty footprints in a shipment of macaroons raised suspicions of "human activity" days before the deaths of 39 migrants in a lorry container, a court has heard.
The Vietnamese victims suffocated en route from Zeebrugge to Purfleet in Essex on 23 October 2019.
The tragedy followed two similar successful people-smuggling runs, jurors were told.
Four men are on trial at the Old Bailey in connection with the deaths.
Boxes of macaroons and Bakewell tarts were transported along with migrants on a cross-Channel trip on 18 October last year, it is claimed.
The consignment was later rejected when haulier Christopher Kennedy dropped it off at Lenham Storage in Sittingbourne, Kent, the court heard.
In a statement read to court, warehouse worker Adam Letwizki, said: "The top layer was nice and clean but the second layer was dirty and wet as if somebody had stepped on them.
"I thought it must have been people. Clean on top, dirty underneath to try to disguise the damage."
Warehouse manager Barbara Richmond-Clarke, who inspected the load, said the crushed boxes and footprints "confirmed to me that there had been some human activity in the trailer that was not legitimate".
Earlier, jurors watched CCTV of an alleged successful people-smuggling trip.
On 17 October, driver Eamonn Harrison was captured on film dropping off a trailer - allegedly containing the cakes and migrants - at the port of Zeebrugge.
During the journey, the temperature in the container rose, peaking at 25.2C, an indication of the extra body heat, it is claimed.
Jurors were also shown footage of Mr Kennedy's truck in the loading area at Purfleet.
Mr Kennedy denies being part of a people-smuggling conspiracy with fellow haulier Eamonn Harrison, 23, of Mayobridge, Co Down, and Valentin Calota, 37, of Birmingham.
Alleged key organiser Gheorghe Nica, 43, of Basildon, Essex, has admitted the conspiracy but denies 39 counts of manslaughter, as does Mr Harrison.
The trial continues.