Over 1000 bike riders rode 13 kilometres around Kew Boulevard to protest against someone who had been laying tacks on the road. Credit:Paul Jeffers The cyclists have various hunches on who the culprit is. It could be a car loving-local or perhaps a frustrated dog walker, or even a fellow cyclist intent on causing havoc -- the ultimate treachery. Those under attack are sure it's part of a long-running vendetta against cyclists who ride the boulevard. In the hunt for clues, some have taken to trawling for anti-cycling comments posted on news stories. "They're sending a message, who knows what that message is," says forensic psychologist Dr Lisa Warren.

"There is no such thing as random behaviour. People do what they do for reasons, even when those reasons are very irrational." What we do know is that the tacker is brazen, happy to operate in plain sight with complete disregard for the consequences of his actions. And obsessive. It's estimated that hundreds of thousands of spikes have been dropped along the 13 curvaceous kilometres of road that hugs the south side of the Yarra as it runs towards the city. As soon as VicRoads cleans them up, it seems, he's at it again. Even a protest ride organised by cyclists earlier last year was tacked. If the Boulie Tacker is an obsessive, so are his hunters. Leading the chase is George Mihailides, a cyclist who has made catching the offender his personal mission.

But George (that's him in the Tour de France headband below) senses he is fighting an adversary who is playing games, baiting cyclists, toying with him personally. He worries that he himself is under surveillance, not by the police, but the culprit. He frets that a Facebook group set up to raise awareness has been infiltrated. Fed-up, he is pushing for the police to up their surveillance on the road, including installing video cameras to catch the tacker red-handed. "I have got an army of cyclists that want to help," he says.

"I've said to police: you want people on the boulevard, hiding behind bushes? We're ready to help you. I could put people on this 24/7 for months." So far, the police have resisted those calls. They do have an investigator on the case full-time but have yet to come up a decent lead or a suspect. Senior Sergeant Mark Standish sits at his desk at the Kew police station, frustrated that he hasn't cracked the case. The tacker is probably operating under the cloak of darkness, he says, with no discernible pattern of when the pins are dropped or where. All police operations, including roadblocks on the boulevard with number plate recognition, have so far been unsuccessful. But police remain confident the tacker will make a mistake.

"The longer it goes, the more chance we are of apprehending them," the lawman says. One theory centres around the nails themselves, which are known as 'blue cut' tacks to upholsterers and furniture craftsmen. Detectives have tracked the supply route, contacting sellers looking for someone buying up big on similar nails but have so far come up empty. Some suspect a second-hand furniture dealer or collector, or an antiques salesman. A tradesman with the means of acquiring lots of tacks. One supplier said amassing such a hoard would take "years and years and years". You'd think it'd be easy enough to find the culprit. A big fat stretch of road in a prime swathe of inner urban real estate. One of Melbourne's most famous stately homes, Raheen, is a stone's throw away.

But no. For its city location, the boulevard feels quite remote (as you can see in the gif above). It's surrounded by bushland, there are few houses overlooking the route, long stretches without much traffic. There aren't many places to conduct a proper stake-out, although that hasn't stopped the cyclists from trying. So for now it is a matter of cleaning up after him. On a grey, blustery December Friday when The Age visits the boulevard, a man in a white ute drags around a mat specifically designed for aircraft runways and military use. Beneath that black mat are five large pockets, scooping up litter strewn across the road for further inspection. A broom-shaped magnet is run across the leaves and debris, picking up any barbs found along the way. The mat, part of a clean-up effort which has so far cost over $100,000, has just picked a dozen up off the path - and that was a quiet day.

The sweeper also believes he's being watched. No sooner does he clean the road and more rusty nails appear. "A lot of times I finish at 2-2.30pm, he watches me and by 5pm we've got more tacks," he says. Some cyclists have drawn comparisons between the tacker and the infamous "hedge burner", who terrorised residents and gardeners of Melbourne's eastern suburbs in a fire bug spree in the late 1980s. Gregory Aristomeni Anastasiou, also known as "Lucifer", led a gang torching dozens of cypress hedges over a two-year stint. He was eventually caught and convicted.

When hedges started going up in flames again 10 years later, Anastasiou was a suspect. Police cleared him at first, until he offered to help find the culprit and was found responsible for burning hedges again. If the tacker is eventually caught, no one will be satisfied with a slap on the wrist. Charges could range from reckless conduct causing injury all the way through to aggravated litter. "There are better ways to go about voicing your displeasure," says Senior Sergeant Standish. "It is a malicious and ridiculous act."