Police have revealed a man found dead in the Waikato River was “subject to a violent attack” before his body was discovered in the water.

Hamilton man John Wirihana Isaac, 53, was discovered dead in the river on the evening of January 18 by a person passing by in a boat.

Detective Inspector Darrell Harpur today revealed more about the investigation into his killing, titled “Operation Angelo”, including the fact he suffered multiple injuries and had suffered a “violent death.

“He was a son, a father, a grandfather, and a much-loved friend. The circumstances around his death have had a severe effect on his whanau. Someone out there knows who’s responsible for this, and knows what happened. We urge them to come forward and tell police what they know.”

Harpur said Isaac’s movements before his death were still being pieced together, but he was last seen at shops in Nawton, Hamilton about 3pm, 24 hours before his body was discovered.

John Isaac was found dead in the Waikato River on January 18. Photo / Police

He said his body was dumped in the river on the afternoon of Thursday, January 18.

Harpur said it would have been in “broad daylight” when people were swimming at the river.

Harpur said he made two visits to a shop on Avalon Drive when he was last seen.

He confirmed CCTV was being recovered and reviewed, but said there was a period of missing time in the lead-up to the death that police were still keen to account for.

“Our investigation is focusing on the Waikato River and surrounding areas, and the public can expect to see a continued police presence in the area as inquiries progress.”

Isaac was known to police but was not a gang member. He was described as a “home body” who spent much of his day watching television.

The Waikato River near Ngāruawāhia was where boaties discovered the body of the man on Thursday evening. Photo / file

His funeral was held in Porirua yesterday.

“This is a tragic end to a life that should not have been taken. We have a dedicated team working tirelessly to get answers on what happened to Mr Isaac, and to hold whoever is responsible, accountable for their actions.

“We want to hear from anybody who was around the Waikato River area in the afternoon of January 18 and saw anything untoward, especially around any of the bridges between Hamilton and Ngāruawāhia.

“We believe some people will also have photos or videos from recreational activity in the river and the surrounding areas, we ask that you reach out to police to provide anything that can assist.”

Isaac was found about 7pm by a group of people who had taken a boat to the river near Ngāruawāhia, Detective Senior Sergeant Ross Patterson said previously.

Patterson said Isaac was believed to have been travelling around the Hamilton area where he resided and was last seen wearing black cargo pants and a green camouflage pattern T-shirt.

“Police are continuing to piece together Mr Isaac’s movements in the days and hours leading up to his death and are appealing to anyone who may have seen or interacted with Mr Isaac in the days prior to Thursday, January 18.”

“The investigation team would also like to hear from anyone who saw any unusual activity near the Waikato River at any of the bridges between Hamilton and Ngāruawāhia in the afternoon.

“Anyone who was out on the river or its pathways and banks and may have been recording recreational activities or taken photos or video on their phones is asked to please contact the inquiry team.”

People with information can call 105 or make a report online at 105.police.govt.nz by clicking “Update Report” and referencing file number 240119/8775.

Information can also be provided anonymously to CrimeStoppers by calling 0800 555 111.

“This is an incredibly distressing time for Mr Isaac’s whānau who are being supported by NZ Police and Victim Support,” Patterson said.