Armed officers were on the streets today as gardaí stepped up their investigation into the murder of a crime boss and an apprentice plumber.

A murder trial which heard allegations of witness intimidation dramatically collapsed at the Central Criminal Court today when the Director of Public Prosecutions entered a nolle prosecqui.

A key prosecution witness told a murder trial she was frightened when two gunmen men entered her flat last April but denied that she was "terrified" into retracting statements implicating the accused man.