The number of times Ireland looked for help from other countries in solving crimes increased by a third last year.
36% of the requests related to murders, sex offences or child pornography.
Under Mutual Legal Assistance legislation, Ireland can look for help from other countries in criminal investigations or proceedings.
The gardaí may want to ask police to interview witnesses or seize a piece of evidence.
Freedom of Information documents, released to Newstalk by the Director of Public Prosecutions, show this legislation was used 643 times by the State last year - compared to 486 in 2018.
Requests were sent to 61 countries or territories last year.
37%, or 240, were sent to the US.
Of those sent to the states, 18 were in connection with murder investigations, and 65 related to the production or possession of child pornography.
Patrick Marry is a retired detective inspector.
He explained: "The American authorities in recent years have conducted major investigations into child sexual abuse.
"When they conduct their investigations, they find that people are accessing child pornography on a worldwide basis - and Ireland has been one of those countries."
In 2019, 87 European Arrest Warrants were issued for suspects who had fled to another European country.
36 suspects were returned to Ireland from the EU to face prosecution.
