Almost 40% of the agency staff employed by the Police Service (PSNI) since 2002 were former police officers, members of the Justice Committee were told, on 3 October 2012.
Neil Gray, of the Northern Ireland Audit Office (NIAO), was briefing the committee on its report into the PSNI's use of agency staff.
He said the PSNI had spent over £100m on 2740 agency staff, and over 1000 of these were former police officers.
The ex-police officers tended to be engaged for twice as long as other agency staff, an average of 223 days.
"The report does not take issue with the principle of using agency staff, what is does question is how the PSNI has gone about it over the years," Mr Gray concluded.
The committee went into closed session to discuss the report.