For a crime to be marked as detected, at least one suspected offender must be identified and sanctioned. Valid sanctions include charge or summons, formal and informal cautions (e.g. Adult Caution, Juvenile Caution), and fixed penalties (e.g. Fixed Charge Notice, Fixed Penalty Notice) for certain offences. There are some limited circumstances where a detection is allowed but a suspected offender is not sanctioned, e.g. the offender dies before they can be prosecuted, or the Director of Public Prosecutions (DPP) decides that prosecution is not in the public interest. These circumstances are outlined in the An Garda Síochána Crime Counting Rules document.

There are various circumstances where a crime is not considered detected, for instance an investigation has not identified a suspected offender, or there is insufficient evidence to support a prosecution. The time lag between an offence being recorded and a suspected offender being formally sanctioned is influenced by a variety of factors e.g. gathering evidence, awaiting laboratory results or a direction for prosecution. As such, detection rates are a point-in-time measurement (i.e. when the data was extracted) and increase over time as more investigations are completed. This affects some crime types more than others.