The discovery of two bodies inside a container at industrial premises is being treated as suspicious, police have said.
It is likely the bodies, thought to be those of two migrants aged under 30, were inside the crates for some time.
The discovery was made on Tuesday morning by staff at Ferroli, near Burton upon Trent, who were alerted by "an unpleasant smell".
Police said the pair must have been helped to hide by a third party.
Officers said the bodies were found within a wooden transit crate that was part of a consignment of commercial boilers.
The boilers left northern Italy on 5 October and arrived in the UK by ferry at Dover on 8 October.
They were then delivered to the warehouse in Branston where the crates remained untouched until employees became suspicious because of the smell and appearance.
Det Ch Insp Dave Giles said the men had been dead for some time.
"We are almost certain they were helped to conceal themselves amongst the delivery load by a third party," he said.
"In view of this we are treating the deaths as suspicious and will be carrying out a thorough investigation into the circumstances."
He said his thoughts were with the men, who must have been "extremely uncomfortable" in their final moments, and their as-yet untraced family and friends.
"We are treating the men with the utmost respect and dignity, and will continue to do so," he said.