''I am 99 percent certain it was Brett,'' said Clare Bickerton, who lives in the Kata-Karon region on Phuket's west coast.
She said she sighted Brett, 43, on December 1 as he rode his motorcycle along the beach road near the sports stadium in Karon ''looking too big for his bike.''
By then he should have been in California, where his worried parents, Wayne and Lynne Bean, have since raised the alarm.
''It's been going round and round in my mind,'' Ms Bickerton said, '' ever since I heard that Brett had vanished.''
Mr Bean's small bungalow in the Kata Karon district was checked by Phuket police on Wednesday night. Officers found his passport, flight departure information, and an opened map of the Thai province of Udon Thani.
Why would a dependable son fail to catch a plane off Phuket then miss booked flights on from Bangkok to Hong Kong and LA?
Clare Bickerton's theory is that Brett Bean had to leave his bungalow in a hurry, and that he is still hiding out somewhere on Phuket.
''The only thing I could think of is that somebody's after him,'' she said. ''When he rode past me he was wearing a hoodie. He had sunglasses on, and he seemed really focussed.
''He had some plain white plastic bags in his motorcycle basket. I'm pretty sure it was him - 99 percent certain. He's such a tall guy and so his knees are up around his ears when he rides a bike.''
She said it was unusual to see anyone wearing a hoodie on tropical Phuket.
The two friends shared a common love of feeding street dogs in the district and would frequently stop for a chat when they met at the local market on Mondays or Thursdays.
Ms Bickerton believes that when she first met Mr Bean about five years ago he had a Thai girlfriend, but she couldn't recall seeing him with anyone since.
''I hope he's ok, wherever he is,'' she said.
Mr Bean's photograph has been distributed to all police stations in the Phuket region and US Embassy officials have been checking hospitals for the vanished American.
Today he will become one of the first Missing Persons cases to be handled by officers stationed at the new Karon Police Station, one of two that opened on Phuket just yesterday.
The new Phuket police operations centre is just a few metres from the beach road and only a kilometre or so from Kata beach, where Mr Bean was reputed to hang out with other surfers.
He would commute annually between Phuket and the US, where he worked as a ski instructor. He would grow a beard at times, although his hair was usually cropped close.
Ms Bickerton described his appearance as ''stubbly.'' In her experience, he was not much of a traveller, being content to stay on Phuket.
Mr Bean's mother Lynne was due to catch a flight for Phuket today.
Local police and a US embassy warden yesterday dismissed any link between Mr Bean and a body found floating off Phuket on November 23.
Mr Bean is described as having blond hair, blue eyes and fair skin. He is 6 feet 2 in and could be bearded or clean-shaven.
He rides a light grey Honda 125cc motorcycle and has a tattoo on the inside of his left forearm.
Anyone who sights Mr Bean should contact the US Embassy in Bangkok on 02 2054049 or after hours on 02 2054000, or contact Phuketwan via the Comments space at the end of this article.