A man who wrote to his brother's neighbours wrongly alleging that the brother is a paedophile says his action had nothing to do with being cut out of his parents' will.

The man, aged 64, dropped packages in the letterboxes of about 40 neighbours around his older brother's home in an affluent Auckland suburb last weekend).

The man who dropped the packages is now under police investigation himself.

The packages included photos of the brother and his wife, a USB stick containing an interview with the brothers' elderly mother, and a letter printed in large, multi-coloured text alleging that the brother molested a 13-year-old girl.

The girl, now a young woman, says the claims are not true.

The man contacted the New Zealand Herald today after another family member told the paper that the letter drop was a result of the man being cut out of his parents' will.

"It's nothing to do with the family will," he said. "I haven't seen the will and don't know what's happening with the will."

The two brothers are the only siblings in the family and the older brother is the executor of their parents' will.

The man said his brother's alleged offending happened about 20 years ago, but the family did not go to the police at the time because "with a family problem like this you try and not cause more trouble".

But he said he decided to write to his brother's neighbours now because the brother now controls a family trust which owns a house which the young woman at the centre of his allegations is living in.

"It's to bring it to the attention of the public in the area where he lives, about his past, and secondly, to bring attention to what he's done to my family," the man said.

He said he informed police about the issue in December but had not heard from them since.

The young woman who was alleged to have been molested by the man's brother told the Herald on Sunday that the accusation was false.

"I have door-knocked the neighbours to tell them but I don't know where else he has gone so I don't know where to go next to help him," she said.

A police spokesperson said police would not usually say if an individual was under police investigation.

"However we can confirm that police are currently investigating a criminal harassment complaint. There is no further comment at this time while inquiries are ongoing."