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Criminal Records Office Number (CRO)

1 November 2021

To identify a particular person by their Criminal Records Office Number. The unique number is assigned by the National Identification Service(NIS) or from late 1998 by National Automated Fingerprint Identification System (NAFIS) to identify the subject.

Up to 12 characters
Either: NNNNNN/YYD i.e. a 1 to 6 digit serial number (leading zero suppressed) followed by an oblique, a two-digit year part and a check character


i.e. the characters SF (no fingerprints held) followed by a 2 digit year part (39 – 95 inclusive) an oblique a 1 to digit (leading zero suppressed) serial number and a check character.

The numeric part of the CRO/SF number having been converted to a single numeric value (YYNNNNNN for a full CRO Number YYNNNNN for a post-64 SF Number and NNNNNN for a pre-65 SF Number (using leading zeroes for serial part) and passed through the standard Modulus 23 algorithm must generate a remainder value that matches the given check character. Check characters are A – Z excluding I O and S