An american man who killed his Irish neighbour following a feud in California last year has been convicted of second-degree murder and is likely to spend at least 45 years behind bars.

Now the widow of John O'Sullivan – who was gunned down in in August last year – has said she will move her children to Ireland for their own safety.

Last Wednesday, the jury at Amador Superior Court returned a guilty verdict against Ken Zimmerman (57) after hearing weeks of evidence. The sentence will be passed next month.

As supporters of O'Sullivan's wife Krista Clem and her family and those of the accused were told a decision had been reached, a heavy police guard filled the courtroom where tensions had been mounting for some time.

Clem, who has not only lost her husband but her two homes in the wake of his death, said that while delighted at the outcome of the trial, her future lay in her late husband's native Co Kerry.

Describing last week's events, she told the Sunday Tribune: "They called us and said, 'Can you be there in 45 minutes?' They said the jury had a verdict.

"The traditional thought is that a quick verdict is a prosecutor's verdict. They had really only deliberated for one whole day.

"There were people on his side there and we were told not to react. One guy ran out of the courtroom. There was no sound, it was silent. They really laid down the law during the trial: that you have to act with a certain amount of decorum in a courtroom."

Clem speculated that those final moments were the first time Zimmerman had not been confident in court, as he realised he could spend the rest of his life in prison.

"Before the verdict this wasn't hard for him. He was smiling and waving at everyone and that was horrific for me to see that kind of attitude when you are in a proceeding for taking someone's life," she said.

"For the first time yesterday I saw the reaction that was appropriate. He had his head hung down and his hands over his face."

In the aftermath of the conviction, Clem went to a local restaurant with friends where they swapped stories about her husband, and later that night she "had a cold Guinness for him".

Now she is selling the family car in a bid to finance flights to Ireland for her and her children. She said she was uncomfortable residing in the same area as Zimmerman's supporters – who she believed were responsible for removing lug nuts from a front wheel on her car during the trial.

"For me it's a huge relief but you feel that it is not quite over. I feel like I have to get the kids out of here now to know that they are safe," she said.

"With everything that has gone on, I don't trust Ken's supporters to leave us alone at this point. I think it's better to take this precaution."