Up to 20% of complaints about police officers in Greater Manchester are not fully investigated, according to new figures.
The Police Complaints Authority (PCA) report for 2003 was due to be discussed on Friday.
Investigations can be dropped because, among other reasons, a complainant has moved away, says the PCA.
Greater Manchester Police said complaints inquiries are only stopped after consultation with the PCA.
Complaints inquiries can also be dropped for a variety of reasons according to the report.
It could be because someone has a grievance against a particular officer.
It could be terminated, too, because the complainant is repeating a claim already being investigated.
A third reason could be because the person insists on anonymity and wants no contact with the PCA.