Phillip Cottrell, 43, died in an attack as he walked home from his job as a news editor on a radio station in Wellington a year ago.
Nicho Waipuka, 20, who admitted punching Mr Cottrell, was found not guilty of murder but convicted of the lesser charge of manslaughter.
His co-accused, Manuel Robinson, 18, was acquitted of all charges and walked free from court.
Waipuka will be sentenced in February.
Mr Cottrell's sister, Sue Hollows, who sat through every day of the trial at the High Court in Wellington, told of her anguish at the outcome.
She said: "We are extremely disappointed, having heard every shred of evidence before the court. Phil was taken from us in the most tragic of circumstances in an unnecessary and unprovoked attack."
Her husband, Heath Hollows, added: "We don't hold it against the jury, it's the system. We're just disappointed Wellington streets aren't any safer than what they were a year ago. In the hospital for 17 hours I watched my wife hold Phillip's hand. The next day she had to sit and watch him die and it took over an hour and a half. It's just so traumatic what's happened."
The officer in charge of the case, Detective Senior Sergeant Scott Miller, said police were disappointed with the verdict, but added it was too early to say if an appeal would be lodged.
Mr Cottrell, who had brittle bones due to a genetic condition, suffered a shattered skull in the attack as he walked home from work on December 10 last year. He died in hospital the next day.
Robinson and Waipuka had been on trial for two weeks before the judge summed up and the jury returned its verdict after deliberating for about six hours. Neither of the men's lawyers commented following the verdict.
During the trial Waipuka's lawyer, Paul Paino, said his client admitted punching Mr Cottrell once. Robinson's lawyer, Mike Antunovic, said his client was on the other side of the road when the attack happened, and had not encouraged the attack.
Mr Cottrell worked for BBC Scotland in Glasgow before emigrating to New Zealand, where his sister lives, in 2006. He worked as the bulletins editor on Radio New Zealand.
Friends and former colleagues from BBC Scotland said: "Phillip was a gentle, kind man with an impish sense of humour. He was a brave traveller, forever venturing to new countries and exploring new cultures.
"He leaves behind many friends in every corner of the world who will be distraught to learn of his loss. Phillip's friends in Scotland are devastated at his senseless death. Our thoughts are with his friends and colleagues in New Zealand and, most of all, with his family."