A third of all assaults, kidnappings and thefts recorded in 2018 had resulted in a prosecution or sanction by September just gone.
Only one in six burglaries last year have to date being solved, but three quarters of homicides have led to a prosecution or other sanction.
New figures published by the CSO – the first on detections since 2016 – show varying rates for solving crimes, with that for sexual offences the lowest, at 11%.
For other headline crime categories, the detection rates are: Homicides 75%; assaults 32%; dangerous or negligent acts 84%; kidnappings 33%; robberies 26%; burglaries 16%; thefts 33%; frauds 21%; drugs 85%; weapons 75%; property damage 19%; public order offences 81%.
The CSO said the detection rates related to the situation as of September 2019 and that they were likely to increase as time passed.
Within the assault group, just a fifth of attempted murders and around a quarter of murder threats have so far been solved. However, more than four out of ten assaults causing harm have been detected.
Almost four of out ten robberies of banks or financial institutions have been detected, but less than a fifth of cash in transit robberies have been.
While two-thirds of thefts from shops have been solved, just one in ten thefts of a person and only one in seven thefts of a vehicle have been detected.
The figures show that while crime rates (per head of population) are higher in Dublin for most crimes, detection rates are lower.
Dublin had generally twice the rate of burglaries than other regions, but had a detection rate of 13%, significantly lower than most other regions (18-22%), apart from the South East (also 13%).
Dublin’s rate of robberies was five-to-six times that of other regions, but only a fifth have been solved, compared to 30-40% in other regions.
The Northern Region had the highest rates of crimes in many categories, including homicides, sex offences and assaults, but had higher detection rates.
Dublin had the highest rate of thefts, but again had a lower detection rate (30%). The Southern Region had the next highest rate of thefts, and had the highest detection rate (42%).
The CSO and Garda HQ said detection rates, particularly for crimes that take time to solve, such as sex offences and fraud, could rise.
The CSO stopped publication of all crime figures in June 2017 over concerns at the quality of Garda Pulse data. It last published detection data, for 2014, in 2016.
It said its decision to resume publishing detection figures was because of demand and improvements in Garda data quality control.
However, it said all crime data, including detections, was still being published “under reservation”, meaning caution should be taken regarding the quality of it.
Because of the new methods and controls used for detections, the CSO said the figures cannot be compared to previous years.
A Garda spokesman said that tighter data governance within the organisation has led “to an apparent drop in detection rates” for some crimes.
He said the changes made internally mean that the figures are more in line with international norms and made them comparable.
He explained that before 2018 the detection system was manually operated at the discretion of the garda and local superintendent after the evidence was gathered and reviewed.
The spokesman said the training and communication of the rules was “weak”.
He said that since 2018 detection is automatically recorded at a later date, at prosecution or sanction stage, and that no member discretion is allowed. Exceptions, such as cases where the suspect has died, are dealt with centrally.
Deputy Commissioner John Twomey said the fact that the CSO now has confidence to publish detection data was “an important milestone”.
He said this will help give confidence to victims.
In relation to improving the detection rate for sex crimes, he pointed to the establishment of the National Protective Services Bureau and the divisional Protective Services Unit.
He said there are now 12 of them, with another two expected by year’s end and full rollout by next March.