A major inquiry has been launched into allegations that a scenes-of-crime officer conducted sub-standard work, potentially undermining dozens of criminal cases.
The police watchdog said it was managing an investigation into the "quality of work and qualifications" of the 48-year-old man, who was employed by Staffordshire Police and Cleveland Police between 1996 and 2011.
A spokesman for the Independent Police Complaints Commission (IPCC) said the inquiry was examining 90 cases which have raised concern in the Cleveland Police force area, including an investigation into a death which has been reopened.
Confirming that families affected by the 90 cases in Cleveland had been notified of the inquiry, the IPCC said the investigation began in February 2011 when the scenes-of-crime officer was suspended from duty.
The unnamed employee, who resigned from his post last October, is currently on police bail after being arrested in May 2011 on suspicion of perverting the course of justice.
Major Incident Teams at both Staffordshire and Cleveland Police have been working on the investigation, under the direction and control of the IPCC.
In a statement, the IPCC said: "The managed investigation is examining allegations that the man conducted sub-standard work, potentially undermining investigations into a range of incidents including suspicious deaths, and had lied about his qualifications when involved in arson investigations.
"The investigation has so far examined all incidents that the man was involved with and narrowed the focus down to 90 cases where concerns exist in the Cleveland Police force area.
"One investigation into a death in Cleveland has been reopened as a result of the initial findings of the managed investigation."
The scenes-of-crime officer worked for Staffordshire Police from 1996 to 2002, Northumbria Police for a short period in 2002 and Cleveland Police from 2002 to 2011, although no concerns have been found relating to his employment with the Northumbria force.