Humberside Police is being investigated by the Independent Police Complaints Commission (IPCC) over its handling of sex abuse allegations at a care home.
Former principal James Carragher was jailed for 14 years
Five men were charged with indecent assault last year after allegations of abuse at St William's Community Home in Market Weighton, East Yorkshire.
During the trial two were acquitted while three had their cases dropped.
The IPCC will focus on the impact of the case on the lives of the five innocent members of staff.
It will also examine what has been described as serious allegations of incompetence by detectives in the case.
The IPCC investigation was started after Humberside Police voluntarily referred a complaint made by one of the men.
IPCC commissioner Nicholas Long said the allegations, if substantiated, were a matter of public concern.
In a statement, he said four other individuals involved in the case had since made similar complaints against the force.
"I take these allegations very seriously and will ensure they are thoroughly investigated," said Mr Long.
The subject of the IPCC inquiry is Operation Aldgate, Humberside Police's inquiry into alleged abuse at St William's care home between 1969 and 1989.
The principal of the Catholic-run home, Father James Carragaher, was convicted of abuse and jailed for 14 years in December after a trial at Sheffield Crown Court.