Gardai and prison authorities have begun an investigation after a prisoner was found dead in his cell in Wheatfield prison, Clondalkin, last night. The 31-year-old, who was serving a sentence for road traffic offences, was discovered in his cell by prison staff with a ligature around his neck at around 10 p.m. A post mortem is due to take place this morning. The prisoner had been due for release shortly.