Immediately, he knew it was the gunman being hunted by police for shooting dead two Work and Income workers in nearby Ashburton and seriously injuring another.
"He was out in the open, out in the middle of the paddock," a shaken 33-year-old Mr White said.
The fugitive, Russell John Tully, simply looked like a man "who had been hunting", Mr White said.
"I knew who he was straight away. I carried on driving in my ute, away from him, called the police, told them where he was."
Armed officers and police dog teams swooped on the crop and sheep farm near the Ashburton River mouth and upmarket development of Lake Hood.
Tully put up "minor resistance" before dogs latched on to him.
Video: Two people shot dead in Ashburton
The arrest followed a seven-hour manhunt on a day that began like any other in Ashburton.
Office workers poured coins into the parking meters, farmers ventured to town for stockfeed.
About 10am, the tranquillity of small-town business was shot to pieces by gunfire.
Read yesterday's coverage here:
• Work and Income shooting: 'Huge relief' after arrest
• Interview with suspect Russell Tully shows his state of mind
• Ashburton Work and Income shooting: Suspect arrested
• 'I could feel the air whoosh past my head'
• Ashburton shooting: Winston Peters says emails to Tully kept bouncing back
• Roll-call of abuse and attacks at Work and Income
Tully, 48, chained his bike to a stop sign outside the Work and Income office on the corner of Cass and Moore Sts, where he'd been previously served a trespass notice.
Wearing a black balaclava, the well-known loner and homeless man, who had recently been in the local paper pleading for help, walked in armed with a sawn-off shotgun.
Police say he opened fire, killing two workers instantly, and critically injuring a third. A man inside the office, who asked to be called David, was in the midst of an interview when the gunman shot the staff member sitting opposite him, less than a metre away.
The shooter then turned the weapon on another person.
"It was incredibly loud, I could feel the air whoosh past my head," said David.
The gunman walked calmly outside, broke down his weapon into his backpack, and unchained his bicycle. He left his helmet on the footpath, riding east along Moore St.
Video: Police apprehend suspect
David had followed the man outside, swearing at him.
Another witness said he saw a person run from the offices, yelling after the shooter: "You bastard, you've blown her to bits."
Another bystander said a large, "brave" man was shouting at Tully: "I'll f***ing kill you, I'll f***ing kill you."
The man grappled with the gunman, but managed only a thump to the back of the shooter's head before he took off towards the Ashburton River - four blocks away - where he is understood to have been sleeping rough. Then, he disappeared.
Armed Offenders Squad and special tactics group officers rushed from Christchurch, 90km away. Other police came from Timaru. Every Ashburton officer was on the hunt.
Inside the Winz office, horrified staff tried to care for their bloodied colleagues.
A large cordon surrounded the Winz centre; police were tight-lipped.
It soon became apparent that the search was focused on the river.
A helicopter slowly scoured from above. A dark-clad sniper hung out its doors, searching through his high-powered rifle's sight.
Police dogs barked at the riverbed.
Photo / Ashburton Guardian
Bruce Henderson was on his morning run on the Ashburton River track.
As he and his running mate were heading east, a man wearing camouflage clothing and a balaclava sped past them. The track is well used by mountain bikers, but the man looked odd, out of place. "And he was in a real hurry."
All of Lake Hood's 70 or so houses were evacuated after a local woman reported a likely sighting.
A 5km cordon was looped around the locality; armed police waved off cars.
Meanwhile, in Ashburton, police patrol cars zoomed up side streets. Plain-clothed officers strapped Glock pistols to their legs, and peered past street corners.
Canterbury commander Superintendent Gary Knowles fronted a press office outside the local police station at 12.30pm. He confirmed everyone's worst fears - two people had died.
Mr Knowles circulated a photo of the "person of interest" - Tully.
Video: Police hunt for killer gunman
"We are warning the community not to approach him."
Later, Ashburton Mayor Angus McKay was shown a photo of Tully and instantly recognised him.
He met him earlier this year and helped him get housing through Presbyterian Support, who "looked after him very well".
The local paper, Ashburton Guardian, had highlighted his plight of living in a tent.
"Everything has been done to help this individual," Mr McKay said.
The hunt went on.
Mid afternoon, armed police swooped on an abandoned Housing New Zealand property in Willow St.
They yelled that they had the house surrounded, and for the occupants to come out with their hands up.
Smoke bombs were thrown and the rear door rammed. Armed police swarmed in.
"All clear," soon came the call.
There was no sign of the gunman.
Photo / Ashburton Guardian
Fears were rising the shooter would not be found by nightfall.
Another police press conference was held at 5pm: Mr Knowles said the hunt would go through the night - 100 officers were on the case, thermal-imaging gear would be used, no stone would be left unturned.
But about the same time, the police dogs - thanks to the tip-off from Dan White, the farmer - had the scent of their man.
The dogs tracked Tully down Terrace Rd when their handlers unleashed them.
They soon brought the man down.
No shots were fired and there was no stand-off. A gun was nowhere to be seen.
Mr White watched Tully being taken away in the paddy-wagon to Ashburton police station, where he would be medically examined before being formally interviewed and charged.
Mr Knowles said: "Nothing will give the families who lost loved ones closure but I think a community can go to sleep tonight with the thought that the person we believe may be responsible is in custody."
Mr White was relieved, and happy for his wife and three school-age kids to finally return home.
Police thanked him for his help in catching an alleged cold-blooded killer. "If I hadn't gone out to move my sheep, I wouldn't have seen him, and he probably wouldn't even have been found," Mr White said.
