Detectives in Hucknall who uncovered a £1.5 million drugs cache three years ago have admitted they are no nearer to catching the criminals responsible.
Officers made the discovery after carrying out an unrelated search warrant at Alexandra House on Watnall Road, on October 17 2012.
More than 3,000 plants, with an estimated street value of around £1.5 million, were found inside in what is thought to be one of the largest ever drug hauls in Nottinghamshire.
Sergeant Simon Scales, of Ashfield South, said: “A comprehensive investigation took place and we could not link anyone forensically to the grow.
“At the time two Vietnamese illegal immigrants were locked in the premises to look after the plants – feed and water them.
“The CPS did not prosecute the two Vietnamese men as they were deemed to be victims of human trafficking and are protected by European Convention in this regard.”
Inside the building, police discovered a sophisticated set-up with thousands of plants and hydroponic systems.
Over three years later and the ringleaders of the operation have not been caught.
However, Sergeant Scales added: “Even though we could not attribute any one person, what we can say is that whoever it was certainly lost a lot profit, tens of thousands, in the plants and equipment seized.”