A man and a woman, both aged 38, have been arrested in connection with the 39 bodies found in a refrigerated lorry in Essex.
The pair from Warrington, Cheshire, were arrested on suspicion of 39 counts of manslaughter and people trafficking.
It takes the number of arrests made in connection with the case to three, with the 25-year-old driver of the lorry still in custody.
The bodies - all of Chinese nationals - were discovered in the early hours of Wednesday morning in a vehicle parked at an industrial estate in Grays.
Eight of the bodies in the trailer were women, and 31 were men.
The first post-mortem examinations on the victims will begin today, followed by formal identification.
The murder investigation is the largest Essex Police have ever faced, and they said it would take "considerable time to come to a conclusion".