The wealthy jeweller's son accused of murdering his Hampshire student girlfriend in a jealous rage told a jury he never strangled her and only defended himself after she repeatedly attacked him.
Elliot Turner said that an argument in his bedroom turned violent and he was forced to grab aspiring model Emily Longley by the throat to stop her assaults.
He denies murder and perverting the course of justice.
Turner said he had been disgusted by his actions at his house in Bournemouth and wrote a letter to his mother telling her how ashamed he was and that he was leaving for Spain.
Giving evidence for the second day at Winchester Crown Court, Turner, 20, admitted he had threatened 17-year-old Emily, a student at Brockenhurst College, and that he felt ''upset and deceived'' on the night before she died on May 7 last year when he saw untrue emails on her phone saying he had smashed her face into a table.
He told the jury that he was angry about lies others had told about him but admitted that telling his friends he had killed Emily with a mallet two days before she died, and threatening to kill her, was ''childish behaviour'' and would ''look really evil'' but it was "me pretending to be a gangster''.
He denied he had used his arm to strangle her in a ''sleeper hold'' or that he put a pillow over the business studies student's face.
Sitting in the witness box before a packed public gallery, Turner told the jury that he and Emily had argued that night and she had thrown drinks over him but initially in his bedroom they had been ''loved up''.
He said he went outside for a cigarette and Emily did not like him smoking and said his breath smelt like an ashtray and this had started another argument and she had tried to lock him out.
''Emily started going nuts, just trying to throw punches at me, just hitting my back,'' he said.
He said he tried to question her about the emails he had seen on her phone a few minutes earlier and she replied it was none of his business and the pair traded insults with Emily on the bed, he told the court.
He then said she punched him again and he used his forearm to push her back and he made contact with her collarbone and she fell back onto the bed.
Turner then said he told Emily to get out of the house and threw £20 at her for a taxi.
''She just ignored me at first. Then five seconds later she just went crazy. She kicked me in the upper right thigh near to the private area. I said, 'Emily calm down, stop it and this point she was just throwing punches at me and going nuts.
''She started screaming at me, 'I never loved you' and I noticed her self harm marks on her arms.
''In all the time I had known Emily I had never noticed them before and I grabbed her arm and turned it around to see them,'' he explained.
''I said to Emily, 'I really want to look after you. I do not want you to go back to your old ways. When will you understand I only want to look out for your best interests? But I won't be treated like a fool, used and lied to. You tell me in private you love me and reveal your darkest secrets, but to other people it's like you are on a stage and have to perform for them.''
Turner said that Emily then attacked him again.
''I had never seen Emily get to that point of rage. I didn't know what to do. She would not stop. I kept repeating myself, 'stop it, calm down'.
''At that point I grabbed her by the neck using my right hand.''
His defence counsel Anthony Donne QC asked: ''Why did you do that?''
Turner replied: ''To stop her going nuts. I did not know what to do. My right hand made contact with her neck.
Mr Donne: ''How hard?''
Turner: ''I would not say very hard but it was quite hard. I grabbed her and pushed her down on to the bed. I pressed down on her neck when she was in the lying down position.''
Mr Donne: ''How long all together from start to finish did you put your hand on her neck?''
Turner: ''Not long - five or six seconds. I then let go and stormed out of the room.''
Mr Donne: ''Did you intend to hurt her?''
Turner: ''No.''
Mr Donne: ''Did you intend to cause her serious injury?''
Turner: ''No.''
Mr Donne: ''Did you intend to kill her.''
Almost in a whisper Turner replied: ''No.''
Turner said that Emily had said nothing after he grabbed her and he went into the lounge and he was disgusted with himself.
''I told myself when Emily wakes up she will tell my mother and father, so I got a piece of paper and decided to write a letter to my mom.
''I said: 'Dear Mom, I cannot believe how I acted tonight. I'm ashamed I wore my heart on my sleeve tonight. I let my emotions get the better of me. I'm not going to lie. I will tell you the truth, me and Emily had a physical argument tonight. I grabbed her by the neck and threw Emily on the bed. Please forgive me. Emily's either in the room crying or has gone home. Emily will never want to speak to me again.''
He then said he was going to Spain and put the note under his parents' bedroom door.
Turner said he thought that Emily was crying and disgusted with him and when he went back into the bedroom she was still in the same position and he thought she was asleep.
He said he got into bed, that he never touched her and he went to sleep immediately and woke up around 8.30.
''I said, 'Emily wake up, wake up. She was in a similar position. I then walked into the kitchen and said, 'Emily if you want some breakfast just help yourself.''
He said he went upstairs to brush his teeth and came back down and tried to physically shake Emily awake but there was no response.
''I said 'Emily you cannot stay in my bed all day' and I went back into the kitchen.''
He then went back into the bedroom, he told the court, and touched her cheek. ''She was just so cold. Then I sort of froze for 20 seconds.''
His mother then came and tried to wake Emily for several minutes, Turner said, and he went into the lounge and just sat there ''blank''.
''I thought maybe she's in a fever or something. I had never come across anyone cold before. I had no idea.''
His father then came back from the jewellery shop and the paramedics were called.
Turner said he then packed his suitcase.
''I just thought 'Oh my God Emily's dead, just shock'.''
Mr Donne asked: ''Did you think in any way you had been the cause of her death?''
Turner replied. ''I didn't think I was the cause of her death, but I was thinking I'm her boyfriend and we had an argument the night before - this looks really odd.''
Earlier the jury heard the prosecution allege that heavily-built Turner strangled the part-time Topshop assistant and that he was a violent and jealous boyfriend, fearful she was being unfaithful.
Emily was born in Britain but her family emigrated to Auckland, New Zealand, when she was nine.
She had returned to live with her grandparents in Bournemouth, Dorset, to study when she died.
Turner denies murder. He also denies, along with his parents Leigh Turner, 54, and Anita Turner, 51, of perverting the course of justice.
Turner is expected to continue his evidence today.
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