A top level investigation has been launched into the conduct of police officers involved in the inquiry into a shotgun murder.
Lee King died after being shot in Middlesbrough's Park End estate in January, 2000.
The man accused of his murder, Keith McQuade, was cleared by a jury at Teesside Crown Court the following year. Allegations emerged later that Cleveland police had earlier authorised a loan to McQuade to buy a shotgun he wanted to enforce drugs "taxing".
A police probe, Operation Walden, has uncovered further evidence against officers, which will be investigated in a separate probe by an outside force and overseen by the Independent Police Complaints Authority.
Mr King's family were informed of the move by a senior officer earlier this week.
Superintendent Steve Ash, the senior investigating officer on Operation Walden, confirmed that allegations had been made during his investigation.
This had given rise to a spin-off inquiry into "certain aspects" of the Lee King murder probe.
The allegations had been referred to the complaints commission by Cleveland's Chief Constable, Sean Price.
Supt Ash said: "These allegations have to be investigated fully. This will unfortunately cause upset and distress, particularly to the family of Lee King.
"We are very sensitive to their feelings and have visited them on a number of occasions.
"They will be kept fully informed of developments."