It means that, currently, it appears that all possible leads and evidence have been investigated but have not yet led to the identification of a suspect or perpetrator. A "cold case."
Special Criminal Investigation happened in 1989.
Special Criminal Investigation was created in 1989.
Introduction of computerized criminal investigation system
It can mean that the case is still open and under active investigation or prosecution.
Manuel S. Pena has written: 'Criminal Investigation, Practical' 'Practical Criminal Investigation' -- subject(s): Criminal investigation
Ronald F. Becker has written: 'Criminal investigation' -- subject(s): Criminal investigation 'Criminal investigation laboratory manual' -- subject(s): Crime laboratories, Criminal investigation, Handbooks, manuals, Handbooks, manuals, etc
Charles E. O'Hara has written: 'Fundamentals of criminal investigation' -- subject(s): Criminal investigation 'An introduction to criminalistics' -- subject(s): Criminal investigation
Getting all the facts in a criminal investigation, physical evidence, people and records
Jerry L. Dowling has written: 'Criminal investigation' -- subject(s): Criminal investigation 'Criminal Law'
criminal investigation division, part of the Provost marshal element (military police)
Neither phrases are "legal" terminology, but in common-usage they usually mean the same thing.
Steven G. Brandl has written: 'Criminal Investigation' -- subject(s): Criminal investigation