Detectives are appealing for help with an investigation into an attempt to smuggle a massive haul of heroin through Birmingham International Airport.
The drug - worth more than £1.5 million - was discovered hidden in a consignment of air conditioning units. It was seized during a joint operation between HM Revenue & Customs at the airport and Leicestershire Police.
And they now looking into an earlier consignment of the same air conditioning units that came into the airport months before the foiled smuggling attempt.
Detective Inspector David Sandall, of Leicestershire Police, said: "The drugs seized back in July last year were hidden in the packaging surrounding adiabatic air cooling units. We now know that a further 17 units came into the UK via the same route in the months prior to the police and HMRC operation. We believe that the packaging of these units will also have been used to conceal drugs.
"To date we have recovered eight of the 19 units. While we don't believe that the remaining units will still contain drugs, we do believe they are vital evidence in this extremely complex investigation.
"The units could have been dumped or sold for scrap locally. There is also the possibility that people are unwittingly storing them. We believe all of them will be in the Greater Leicester area."