The prosecutor in David Mahon’s murder trial has told the jury that his “suicide by stepfather” theory is a fantastical suggestion.

He also accused him of telling lies following his arrest the day after he’s alleged to have stabbed Dean Fitzpatrick at Northern Cross, Dublin 17 in May 2013.

David Mahon admits holding the knife that inflicted the 14cm deep wound that killed Dean Fitzpatrick but denies his murder.

He claims it was an accident and told Gardaí his stepson may have even wanted to impale himself on the blade.

In his closing speech, Remy Farrell, SC for the DPP, said this case is about a split second and told the jurors they’d have to figure out what was in Mr. Mahon’s mind during that split second.

Did he intend to kill? Or to cause serious harm? – he asked.

He said they would have to look at the hours leading up to the alleged murder when he was frenetically trying to contact Dean. He asked them to consider his actions afterwards when he left the scene and got rid of the knife.

Mr. Farrell accused him of lying to Gardaí. He said the “coldest, most calculated” one was used to cover up the most shameful part of his actions – his failure to call an ambulance.

The jurors will hear from his side on Tuesday.