IT ended with the discharge of a gun and a dead man, slumped over the wheel of a tractor which had veered off the road and embedded itself in a nearby tree.

But it had begun years earlier, when tensions between neighbours over land, horses and property development started simmering under the surface of everyday life in rural Fiddletown, California, in the foothills of the Sierra Nevada mountains.

"There is not a great deal of sympathy amongst the neighbours," said a local resident, mulling over last week's killing of Kerryman John O'Sullivan (47) in the US, whose tragic and unexpected death was the denouement of an ongoing feud.

"A lot of them thought that something like this was going to happen even though a homicide was totally out of character for Ken Zimmerman."

Zimmerman, a 56-year-old neighbour, is currently in prison facing charges relating to the killing of O'Sullivan.

According to police and media reports, a heated exchange between the two men culminated in O'Sullivan driving a tractor through Zimmerman's fence, Zimmerman warning police he might shoot him and, eventually, O'Sullivan's wife calling to say she couldn't find her husband.

O'Sullivan was dead. Zimmerman gave himself up and Fiddletown began the long process of coming to terms with the violent resolution of a protracted dispute.

The Irishman, originally from Valentia, Co Kerry, had moved to the US when he was 21. He was married to Crista and his violent demise also leaves behind a five-year-old son, Michael, and a one-year-old daughter, Tessie.

But for some O'Sullivan was a man whose actions seemed to heighten tensions with neighbours, tensions which, for whatever reason, never seemed to resolve themselves.

A court case surrounding cruelty to animals, a disputed right of way and aspirations of becoming a property developer – many things have been posited as being at the centre of the bickering which last week turned deadly.

In January 2006, O'Sullivan had several horses seized by authorities over claims they were being starved. In March the following year he entered a no-contest plea in court to two misdemeanor charges of failing to provide appropriately for the animals.

They had been seized from his property after a dead colt was discovered by one of O'Sullivan's neighbours. Three others were taken to an animal-welfare centre which described them as being extremely emaciated.

However, O'Sullivan's attorney pointed out at the time that a necropsy report on the dead horse revealed large amounts of larval nematodes. Others say O'Sullivan was adamant that he had not mistreated his animals and that the dead horse had been the victim of parasites and disease.

Concerns

O'Sullivan's interest in property development had also led to tensions. Since around 2002, his planned Mokelumne Bluffs housing development – consisting of 98 units – had led to several planning meetings and concerns, perhaps normal with any such project.

While in August last year he had been granted approval, how close he had actually come to realising the dream remains unclear.

At the time of sanction, O'Sullivan told a local newspaper: "As soon as we get final map approval we'll be starting on the roads in phase one. Cognisant of the possibility of delays caused by the process or the weather, we'll definitely start by next April." However, just four months after that prospective date, O'Sullivan would be dead.

"He was a controversial figure in the area not just because of the horses but because he had dreams of becoming a big developer and it is a very anti-development area here," said a local, summing up many people's mood towards Mokelumne Bluffs.

"He was in the process of trying to establish some pretty big developments over here. I don't know how he would have got the financing but he had begun the process of going through the permit system."

Last May, O'Sullivan upped the stakes in his three-and-a-half-year horse-neglect case when he decided to sue Amador County for rights violations, namely malicious prosecution, seeking unspecified monetary damages.

But in spite of all of this, it seems that a simple neighbourly row, allowed to swell out of proportion, would lead to O'Sullivan's fatal shooting.

Smashed

At around 7.45pm local time last Sunday, emergency dispatchers got word that a heated fight was getting out of control. Zimmerman informed the authorities that O'Sullivan had smashed through his gate on a tractor and slapped him in the face. They had better get there before I shoot him, he said.

"There was a legal right of way which Zimmerman legally had the right to use to get to his land but it crossed O'Sullivan's land," explained someone familiar with the dispute that many believe was at the centre of the killing.

"After the neighbours turned him in for the horses he put up this fence and locked it so that Zimmerman couldn't get on to his property. They say it was done in spite, that they were arguing for about three years and at one time Zimmerman drove his truck through the fence. What happened on that night, no one is very sure."

These exact circumstances will only become clear when Zimmerman's version of events is made public, as the only known witness.

Speaking to the media last week, O'Sullivan's brother Brian said he believed he was simply going over to try and end their row.

"John didn't go over there with a gun. Can anyone honestly say he waited at the gate after this altercation for Zimmerman to come back with a gun and shoot him?" he said.

"We believe John went over there to sort it out."