The stepbrother of cabinet minister Nikki Kaye has been charged with first-degree murder in California.
Clinton Thinn, 29, could face the death penalty if found guilty.
He is being held at George Bailey Detention Facility in San Diego, following his arrest last June over a bank robbery.
Local media reports at the time said he walked into a Bank of America holding a claw hammer and a flare gun.
A charge sheet from the local sheriff's office shows that he has since been charged with murder.
The Ministry of Foreign Affairs and Trade said in a statement they were aware of Mr Thinn's situation and were giving advice in relation to the robbery charges.
Mr Thinn is Associate Education Minister Nikki Kaye's step-brother.
In a statement from her office she said it was "a difficult and sad time" for all those affected.
"As this is before the Courts, I will not be commenting any further"
Mr Thinn's Facebook page says he attended the prestigious Auckland Boys Grammar School, in the upmarket suburb of Epsom, and Selwyn College, in Auckland's eastern suburbs.
A YouTube channel in his name hosts numerous videos of Mr Thinn rapping.
He travelled to the United States in May last year.
He is due to appear in court on 27 February on the robbery charges. The court date set for the murder charge is 6 March.