Detectives rushed to the Jelfs Rd property on Thursday after reports a body was there.
But it took them two days, and intense specialist searches, before they finally discovered it.
A former schoolmate of Johnston is shocked by his friend's death.
"I was talking to Ollie two weeks ago," said the friend, who wished to remain anonymous.
"He'd just moved into a flat and seemed in a good space."
Johnston was a keen outdoors man who loved treks and biking. He'd been in the St Andrew's College road cycling team.
He was described as "very independent" but someone who had "got lost along the way" in the life.
He'd been hitch-hiking a lot recently around the South Island on his own.
"Ollie was obviously just a lost guy. But I can't believe this has happened to him. He was a great guy. It's just the worst news ever," the friend said.
His family did not wish to comment.
Today, there was still a large police presence, and cordon, around the Jelfs Rd property, with officers still piecing together their case.
Horses graze in the front paddocks and across the road is Birchbrook Equestrian Centre.
Woodend Beach and its surrounds is a popular area for horse riders and trainers.
Locals are shocked by the homicide probe.
"It's not what you expect to see. It kind of makes you feel sick," one said.
