National MP Nikki Kaye says her step-brother being found guilty of killing his prison cellmate is "a really tough situation."
Clinton Thinn, 31, was found guilty at trial of killing Lyle Woodward by strangling him with a prison shirt, US media reported.
Kaye said she did not wish to say much because of the legal implications.
"It is an incredibly sad and difficult time for all of the families affected by this.
"This is a really tough situation and obviously I'm in contact with my family. It's difficult because it's really tough but it's all really important that there could be legal considerations and that anything that I say could affect that."
Thinn asked for a nurse to check on Woodward who was found lying in his cell on December 3, 2016.
He died a week later.
The former Auckland Grammar School student was behind bars after being charged over an attempted bank robbery in Chula Vista, near San Diego.
Through his lawyer, Thinn argued he was defending himself against Woodward.
However, a jury of seven women and five men found him guilty. The maximum sentence he is facing is 25 years to life in prison.
He is still facing charges of assault with a deadly weapon, attempted robbery, making a criminal threat, false imprisonment and burglary.
Neal Putnam, a reporter for the Star News, said Thinn showed little reaction as the verdict was read out.
It was the second trial for Thinn after a jury in February couldn't decide what to convict him of, eventually settling on a hung jury.
An old schoolmate previously told the Herald that Thinn had gone through some personal issues over the years and had been failed by those around him.
After his mother died he inherited a large amount of money and bought an inner-city apartment as well as a Mercedes.
In an interview, Thinn said he wanted to make his home a unique and hip place to live.
"I decided to make some alterations and put a fish tank in the wall to make the apartment feel alive as opposed to a sterile hotel environment.
Thinn, a lover of hip-hop and rap, often posted videos of himself rapping to lyrics he had written under the rap artist name: BigMac and Richochet Rocket.