In 2018, RTS said it had discovered alleged manipulation of data within its laboratory processes in Manchester and immediately reported the suspicions to police and the Home Office.
The County Antrim-based company said it had employed staff who had been working at other accredited laboratories and some of those workers had been under police investigation.
As part of its co-operation, RTS said it was helping pay for the re-testing of samples.
Announcing the decision to drop its investigation, GMP confirmed the seven suspects would face no further action.
Assistant Chief Constable Rick Jackson said the decision “had not been taken lightly” and did not rule out the possibility of reopening the case if the “required resources and technology” became available.
He said: “This is, of course, frustrating for people across the country whose lives have been affected by civil, family, and criminal court cases which have relied on test results from these companies and could have been miscarriages of justice.”
