The FBI makes a specific distinction between an offender with sequence number 01 and all unknown details versus an offender with sequence number 00 (and no data entered). If there is an offender 01, that means that the police know for sure that there was just one offender. The example the FBI has CCTV of an offender, but you can't make out any details of that person.
If the police know nothing about the offender or offenders (including how many were involved), the file should contain an offender segment with sequence number 00.
Notice for error code 070 - THE CORRESPONDING OFFENDER SEGMENT MUST EXIST in an uploaded incident report: To avoid this error, any Offender Numbers in the Victim segment (level 4) must exist in the Offender segment (level 5).