Jonathan O’Driscoll (21) typed the words ‘murder in Charleville’ into an online search prior to stabbing his nine-year-old twin brothers to death.
Examinations of his computer and mobile phone gave gardaí an indication of his “state of mind”, Det Supt Sean Healy told an inquest into the three deaths in Mallow.
He also conducted another online search with the words ‘Irish Law, stabbing with a knife’, the inquest heard.
A third search of the ‘science of suicide by hanging’ was found on his laptop, Det Supt Healy said.
The inquest heard how Jonathan O’Driscoll, who was fostered by Helen and Thomas O’Driscoll when he was three days old, doted on his younger brothers.
He grew up in a “loving and caring home”, was officially adopted at 15 and was healthy and happy until he was involved in a road traffic incident in 2012.
After this incident, his behaviour changed and he grew quiet and depressed. He was badly affected by the break-up of a relationship and his mother described him as heartbroken.
“He was quiet in himself, he was heartbroken after her,” Mrs O’Driscoll told the inquest.
Jonathon O’Driscoll grew curious over his birth family and began to believe his adopted mother Helen had information she was not sharing with him.
“He pushed me against the wall. It was out of character but I wasn’t going to take it,” she said.
She said she obtained a barring order against her son, but it was lifted after 10 days because he was “crying and ringing to apologise every day”.
The inquest heard how doctors became concerned for Jonathan O’Driscoll’s mental health and he was prescribed anti-depressant and anti-psychotic medication.
However, a postmortem revealed no evidence of medication in his system.
Consultant psychologist Dr Robert Burns said the medication had helped. "But like many young men he stopped taking the medication and became unwell again prior to his death," Dr Burns said.