Auckland Police carried out two search warrants as they continue to investigate the death of American PhD student Kyle Whorrall

He died following an attack at a Meadowbank bus stop in April - a 16-year-old's been charged with murder, and a 33-year-old woman with being an accessory after the fact.

Earlier this week, Police revealed they'd found a machete at a Glen Innes reserve - which is undergoing forensic testing.

Whorrall's mother Carole is imploring anyone who has information, no matter how small or insignificant, to come forward.

She says their courage could make all the difference.