A 36-year-old man has pleaded not guilty to murdering his ex-girlfriend in a Dublin hotel, after posing as another man on Facebook, to set up a meeting. 

Eric Locke admits killing 30-year-old Sonia Blount in February 2014, but the court heard the issue for the jury would be his state of mind at the time.

Ms Blount's body was found in a room at the Plaza Hotel in Tallaght on 16 February 2014.  She had been asphyxiated and strangled.

Mr Locke admits causing her death, but told gardaí he did not intend to kill her.

The jury was told it would be dealing with the defence of diminished responsibility.

Prosecuting counsel Remy Farrell told the jurors Mr Locke and Ms Blount had a relatively brief relationship and had been seeing each other for a couple of weeks before the relationship fizzled out in early January 2014.

He said it became clear that Mr Locke did not take the end of the relationship very well.

There was a threat of suicide, he said, and he continued to send text messages for a considerable period.

He said Mr Locke seemed to be very unhappy when Ms Blount blocked him on Facebook and stopped communicating with him.

On 15 February 2014, Ms Blount was celebrating her young son's birthday and was then going out. 

She believed she was going to meet a man called 'Shane Cully' with whom she had been exchanging messages on Facebook.

Mr Farrell told the court the contact started with "banter" and then became more intimate. He said there was a suggestion they meet for a sexual encounter.

Mr Farrell told the jurors it was important not to judge and while they may feel it was unwise, Ms Blount was not on trial in any sense in this case.

The court heard Ms Blount went to the Plaza Hotel and 'Shane Cully' messaged her asking her to ensure a key card was left at reception for him. 

But Mr Farrell said there never was a 'Shane Cully' and Mr Locke arrived at the hotel with cable ties, masking tape and an air gun. 

The prosecution says these items were brought to overpower and dominate Ms Blount. 

Mr Locke was caught on CCTV leaving the hotel at 5am and dumping something in a drain. Mr Farrell said this turned out to be a mobile phone which helped gardaí reassemble communications with Ms Blount.

Ms Blount's body was found in the room that morning. She had been asphyxiated and strangled.

A ligature mark on her neck was consistent with a cable tie, the court was told.

Mr Locke admitted he had strangled her, but told gardai that she had been distressed by the items he had brought, that he panicked and strangled her but did not mean to kill her.

The jurors were told they would see text messages demonstrating the "arc of their relationship" as well as the messages from 'Shane Cully' on Facebook which the prosecution says are evidence of intention and planning by Mr Locke.

They were also told Mr Locke would be pleading a defence of diminished responsibility where he would be claiming he was suffering from a mental disorder at the time of the killing to such an extent that it substantially diminished his responsibility for what he did.

The jurors were told the defence would have to prove that part of the case on the balance of probabilities and they would hear evidence from psychiatrists.

Mr Farrell said this was not a case of "who done it", they were going to be asked to concentrate on the mental state of Mr Locke.