A senior City executive and “totally devoted father” killed his two-year-old daughter by smashing her head against the floor because he believed she had been taken over by a “malign and satanic entity”, a court heard today.

Alberto Izaga, 36, the most senior executive in London for the insurance giant Swiss Re, thought he was on a mission and that there was a struggle between good and evil and the devil, the Old Bailey was told.

Mr Izaga, who had described his daughter Yanire as the “most precious treasure on earth” was rambling for several hours in June last year, after waking up in the early hours of the morning, about how executives were part of a sect and were taking over the financial world and an American film called Bug, about a man who had bugs beneath his skin.

With his terrified wife trying to ring for help, Mr Izaga grabbed his daughter from the nursery he had prepared and shook her before swinging her against the wooden floor.

The incident happened after Mr Izaga returned from a business trip to Geneva, where senior colleagues said he had seemed stressed and distracted. On arriving home at his flat, overlooking the Houses of Parliament, everything seemed to be normal — Yanire ran into his arms and his wife Ligia, greeted him warmly. The family went out together for dinner, but his wife remembers seeing him talking to himself.

That night the family went to bed, but he woke his wife at 4.30am and rambled for hours about the sect and talked about the philosophy of the Jesuits, the court heard.

Jonathan Rees, for the prosecution, said that Mr Izaga was still rambling after 6am and told his wife that he had not slept for three days. She asked him to stop and go to bed, which he did but was unable to sleep and began crying and hitting his pillow before getting up and shouting.

When his wife asked him not to wake their daughter he went into her nursery, picked her up and began to shake her as his wife begged him to stop. He did and they sat together on the couch, the baby lying on her father's chest, but he began to shout about the film Bug again. His wife tried to leave the flat to get help but he blocked her path.

He then assaulted his daughter. She did not die straight away, but suffered multiple skull fractures and brain damage and was declared dead two days later.

When police arrived he just kept muttering: “Big Ben, Big Ben” over and over.

Mr Rees said: "Mr Izaga was the most senior executive in London for Swiss Re. He was a doting husband and father. He was the last person you would think capable of killing a fellow human being, much less his own flesh and blood.”

Talking of the attack Mr Rees said: “He picked up his two-and-a-half year old daughter and in a frenzy smashed her head against the wooden floor in front of his wife.

“Even with the benefit of hindsight it is difficult to detect the defendant was going to lose control in the way that he did.”

During cross-examination Dr Timothy Exworthy, a consultant psychologist, agreed that Mr Izaga believed he was involved in an act of destroying a malign and satanic entity, the Devil or something of that nature.

During the incident his wife secretly made several mobile telephone calls for help and the transcript of some of what could be heard on messages she left was read out to the court. She is heard screaming, crying for help while the defendant says: “Please die, Please die.” In Spanish he calls out the word death.

During another message he is heard saying: “Bitch, this bastard does not die.” In another: “God does not exist, universe does not exist, humanity does not exist. I just want to sleep, it's the only thing I want to do.”

Mr Izaga, dressed in a smart suit and sitting with his defence team in the well of the court, followed the reading of the transcript, occasionally taking a sip of water. He spoke only to deny the murder in June last year.

His wife, mother and father were also in court and visit him every day in the medium secure unit where he is being held.

The judge told the jury that this was a unique case and although both the defence and prosecution agree what happened, a jury verdict was required by statute.

Mr said: "Mr Izaga was universally liked and admired by those who knew him.At home he was a doting husband and father who played a full part in domestic life notwithstanding the demands of his job.

"And yet around 8am on June 3 2007 the defendant picked up his two-and-a-half year old daughter and in a mad frenzy smashed her head against the wooden floor of the flat in front of his wife."

He added: "In this case the prosecution and defence are agreed that there is only one proper verdict for you to return in this case and that is a 'special verdict' of not guilty by reason of insanity. This is a verdict that is not often encountered in the criminal courts although, for reasons which will become clear, it is a verdict that is wholly appropriate in this particular case"

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