Witnesses saw a man believed to be missing Australian tennis coach Paul Arber in the Waikato River early on Sunday, police say.
Detective Inspector Karl Thornton said two members of public contacted police today.
They said they had been walking home from central Hamilton across the Victoria Bridge about 4am when they saw a man in the river.
They told police they walked to the river bank and talked to the man. He said his name was Paul and he was in Hamilton for a tennis tournament.
The witnesses told police the man walked out of river then went back in again. He was wearing shorts.
Thornton said the man's behaviour was out of the ordinary.
"The pair offered to take him back to his accommodation but after he has gone with them up to the bridge he has changed his mind and walked off back to the river," Thornton said.
Arber's parents, Sam and Richelle Arber, arrived in Hamilton from Melbourne on Sunday.
Arber had been exhibiting behaviours that were "out of character" shortly before he disappeared, Thornton said.
"There was not any one thing that caused specific concerns but such behaviours present a challenge for searchers trying to map out possible behavioural problems that could help us find Paul," he said.
A 'GENTLE SOUL'
The Arbers have told police their son was a "gentle, spiritual person" who was harmless towards other people, Thornton said.
He is a vegan who drinks only bottled water.
"That is why, like any mother, Richelle Arber is imploring anyone who may have information on Paul's whereabouts, even if it's just something that seemed out of place, to contact police."
Police earlier today upped the search for clues, with a river and airborne search.
Officers today conducted a search by both boat and ground along the banks of the Waikato River from Hamilton East. A police helicopter was seen hovering over the Cook and Grey streets area where Arber was seen on Saturday night.
Police hold grave fears for him
Arber was coaching eight young tennis players competing in the Waikato Christmas Junior Tournament at the Waikato Tennis Centre in Dey St.
He was part of a wider group of about 50 Australian coaches and players.
After a busy day of tennis on Saturday, the group drove to get dinner at the various food outlets in Grey St about 8.30pm.
They agreed to meet back at the minibuses, which were parked in Cook St, at 9.30pm.
Everybody else was there on time, but Arber never showed.
Nathan Hude, a friend of 28 years, said he had been walking with Arber in Grey St when they parted ways.
He saw him stop at an ATM where he believed he withdrew money.
Another friend, Kanga Tennis Tours international director Mark Sheppard, said Arber gave $20 to a homeless person.
Police said Arber had also been seen to stop and pat a couple's dog in the moments before he went missing.
"We just had this huge concern because he's normally a really reliable guy," Sheppard, a friend of seven years, said. "There's no way he'd ever leave his eight kids unattended at the bus."
Arber's wallet and keys were found about 300 metres along Cook St, Sheppard said.
The minibus was left unlocked.
Sheppard said four coaches searched the streets until about 11pm when they reported Arber missing to police.
A police caravan was parked in Grey St yesterday and today with a photo and description of Arber and a dummy modelling the clothes he was wearing.
Sheppard described Arber as a "spiritual, nice person" and an elite tennis player.
"He's just a really good athlete and just a magnificent person," he said.
"If anyone knows where he is, just let us know, just let him come back to us. We just want him back with us."
News of Arber's disappearance has quickly spread through the Melbourne tennis community. A Facebook page has been set up to share information between family and friends.
Waikato Tennis Centre chief executive officer Leslie Wilkinson, organiser of the youth tournament, told the Waikato Times that the incident was upsetting.
"I think we're all finding it difficult. It's really upsetting to have a foreign group here and to have this sort of thing happen. You sort of feel almost like a guilt that it's happened to him when he's in your area. It's an awful feeling."
Arber was the winner of the 2012 Victorian Jewish Tennis Championship.
He has previously worked with the Australian Institute of Sport and the National High Performance Academy. His website states he has coached several elite juniors and professionals including Bernard Tomic, Justine Henin, Monica Seles and Caroline Wozniacki.
Arber is described as a slightly built Caucasian, 179 centimetres tall with short dark hair. He was wearing a grey tracksuit with a tennis logo on the left breast of the top and the Wilson logo on the left shoulder.
Can you help? Call the Hamilton police station on 07 858 6200, or Crimestoppers anonymously on 0800 555 111.
- Waikato Times
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