Crown prosecutor Kieran Raftery said the murder of Mrs Yang was made worse by the fact that the grandmother was in her own home and vulnerable.
"Some two weeks after the murder of Mrs Yang, undeterred by the fact that he [Ah You] had actually killed somebody in a home invasion, he confronted the 34-year-old victim looking after a child.''
Mr Raftery said Ah You had a history of violence that went back to 1998 and included convictions in Australia, one of which was for aggravated robbery.
Court documents obtained by APNZ show that in May 2009 Ah You was sentenced to 12 years in prison with a minimum non-parole period of eight years after pleading guilty to two charges of aggravated robbery and three of robbery.
One of the attacks happened while he was on the run from police, less than a fortnight after Mrs Yang was killed.
According to the documents, a 34-year-old woman was looking after a four-year-old when Ah You broke into her Mangere home on June 27, 2008.
Ah You told the woman he knew her husband, and had come to get some money that was owed to him.
He pointed a pocket knife at her before grabbing her and dragging her into the lounge room where he put her in a headlock. He stole jewellery, money and a cordless phone.
Ah You was also involved in four other attacks. In September 2007, he and another man walked into a house in Clendon, south Auckland, where a tiler was working.
Ah You pushed over the tiler and continued to punch and kick him until he was dragged off by the other man.
The tiler suffered cuts and bruises to his head, a fractured skull and a broken knee that required surgery.
Mr Raftery said Ah You was still "very dangerous'' and the court had to look at his previous convictions when sentencing him for Mrs Yang's murder.
Ah You's lawyer Shane Cassidy said his client never meant to kill Mrs Yang and was trying to put her in a wardrobe so she could not get help. Ah You also disconnected the telephone before he left Mrs Yang's home.
He said Ah You was sorry for what he had done and had told a Corrections officer "I just wanted to get out. I didn't want to hurt her. I panicked and freaked.
"It was all my fault. I accept that what I say isn't going to change what happened. I know inside my heart that coming to jail was a good thing.''
In her sentencing, Justice Pamela Andrews told Ah You that Mrs Yang was clearly no match for his age and strength.
Justice Andrews said Ah You had written her a letter to say he was sorry for what he had done and that he would get all the help he can while in prison.
"I'm prepared to accept, Mr Ah You, that you may now finally feel genuine remorse. However, I find it difficult to reach a conclusion to allow any discount in your minimum term of imprisonment.''
Ah You's trial lasted two weeks at the High Court at Auckland in November. It was the second time he was tried for the crime.
At his first trial, the jury were told of Ah You's previous convictions. He was then sentenced to life in prison with a minimum non-parole period of 20 years, a sentence that placed him among the country's worst killers.
However, his lawyers took his case to the Court of Appeal who found that the jury should not have been informed of his previous convictions, and ordered a retrial.
