A suspect is being questioned over the discovery of a man's body in Rathfarnham in yesterday.
The body of the 42-year-old man, who has not yet been named, was found at his home at Loretto Court in Rathfarnham at around 3 p.m.
A post-mortem is being carried out.
The arrested man is being held at Rathfarnham Garda Station in Co Dublin.
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Gardaí are also treating as suspicious the death of Mary Whelan (27), whose body was found in her home at Clonard Street in Balbriggan in Co Dublin.
Her body was found at the bottom of stairs.
A post mortem was carried out by Assistant State Pathologist Dr Marie Cassidey.
The results are not being released for what a Garda spokeswoman said were operational reasons.