A 30-year-old man has been sentenced to life in prison after being found guilty of the murders of two brothers who were brutally beaten to death in Castlebar, Co Mayo four years ago.

Alan Cawley, with an address at Corrimbla, Ballina, had admitted killing Jack and Tom Blaine but denied the charge of murder.

He claimed he was suffering from a number of mental disorders at the time giving rise to a defence of diminished responsibility which could reduce murder to manslaughter.

Psychiatrists for the prosecution and the defence agreed he had a number of personality disorders but disagreed on whether or not they amounted to mental disorders as required by law to allow a defence of diminished responsibility.

The jury was told the two brothers who were "harmless and well loved" shared a home in Castlebar.

Both had special needs and were physically and mentally vulnerable.

They died in horrific, violent circumstances.

They were subjected to a vicious and prolonged assault by Cawley and died from multiple injuries.

One of the brothers also had boiling water poured on him.

Neither died immediately.

The State Pathologist said the brothers had been subjected to "extreme violence", something the pathologist referred to as "overkill" where numerous injuries are inflicted, far more than necessary to subdue or kill a person.

One of the men was assaulted while lying in bed, the other while lying on the ground.

Their bodies were found in the early hours of 10 July 2013 by a woman who had previously cared for them.

Cawley had recently been released from prison and had been drinking and taking drugs that day.

The prosecution said Cawley had seen an opportunity when he saw Jack Blaine making his way home late at night having gone to a pub across the road from his home for a cup of tea.

Senior Counsel Denis Vaughan Buckley said Cawley had made a decision to kill the brothers in acts of extreme violence.

He said expert witness for the prosecution had agreed Cawley had two personality disorders but these were not mental disorders under the Criminal Law Insanity Act as required for a defence of diminished responsibility.

The psychiatrist for the State said he had acted impulsively while extremely intoxicated and was aware that he had a propensity for such behaviour, having a long history of violence while using alcohol and drugs.

Mr Vaughan Buckley asked the jury to find him guilty of murder.

Defence Counsel Caroline Biggs told the jury the disgust and hatred for what her client did to two physically and mentally vulnerable men was palpable in the room.

She said her client had a life of torture, having been first seen by a psychologist at the age of four and first admitted to a psychiatric facility at the age of 11.

She said he had a mental disorder and had been on medication for years.

She reminded the jury that a psychiatrist witness for the defence said the accused man had two personality disorders along with ADHD and in his view these were mental disorders which would have diminished his responsibility.

Ms Biggs said days before the killings he had been released from prison with no prescription for tranquillisers.

She said he was not in the same category as people who get drunk and do reckless things.

She asked the jury to return a verdict of manslaughter on the grounds of diminished responsibility.

The trial judge, Mr Justice Paul Coffey, told the jury it would have to decided if the mental disorders described by the expert witnesses were mental disorders within the meaning of the 2006 Criminal Law Insanity Act.

He said if they were satisfied the accused had a mental disorder the jurors must then decide if it substantially diminished his responsibility for the acts.

This had to be done once they subtracted any element of intoxication, the judge said.

After deliberating for one hour and 42 minutes since yesterday, the jury returned unanimous verdicts this afternoon.

In a victim impact statement, Paul Dunne, a cousin of the Blaine brothers, told the court that Jack and Tom Blaine were two brothers with special needs and mental health issues.

Mr Dunne said Jack Blaine had a speech impediment, was partially blind and could hardly walk.

He said the brothers would go around Castlebar minding their own business.

"They never wanted a fuss and would tell everyone everything was alright," he said, adding: "but if anyone had to do anything for them, they knew how to say thank you, you should not have bothered."

He said the people of Castlebar kept an eye out for them and were very sad to see the darkness in their house in the evening.

He said the men did not bother with television or luxuries; they were "two simple men, two angels and their deaths shook Castlebar".

Mr Justice Coffey sentenced Cawley to life in jail.

He said the killings in this case were as wanton as they were savage and extended his sympathy to the victims' family.