Number 86, Tritonville Road, Sandymount, always stood out among the grand homes of Dublin's most genteel suburb. There were gaping holes in the roof. There was a huge hole in the floor and cardboard was used to fill some of the windows. Inside it lacked a modern heating system, the occupants preferring paraffin oil.

This outward shabbiness ensured most people kept away. One day a few years ago, however, a man knocked on the door. No answer. He knocked again. Nothing.

After several knocks he heard a dragging sound and objects being moved behind the door. A dark-haired woman came out and peered at him. She then asked him angrily why he was knocking on the door.

He asked if this was Number 96. No it was not, the woman shouted back, and how dare he disturb people at this time of the morning. She asked him several times his name and told him he should not be prying into people's homes. She said she would call the police if he did not leave. She said how dare he call at their home unannounced and sneak about.

Shocked and surprised at this reception, the man turned on his heels, hurriedly trying to find Number 96.

The Mulrooney sisters went back inside and the door slammed.

The story of the man's visit was passed between residents of Sandymount. People felt sorry for the man who had called to the house unawares. Nobody who knew them ever did that.

What distinguished him from neighbours in Leixlip, where their dead bodies were found this week, was he got an answer.

A young boy from Rinawade Grove in Leixlip - hard-up for some summer pocket money - called into the Mulrooney sisters more than a week ago offering to cut their grass.

Looking at their garden he figured they would be willing customers. £10 was his charge. He rang the bell several times. No answer. No sound. He cycled off.

The lack of response may have been because they were dead by then. But then again, few people ever got an answer from the Leixlip house of Josephine (46), Ruth and Catherine (51) and Frances (83), their aunt.

According to Mr David Ryan, of Sandymount Hardware, who knew the Mulrooneys well, many workmen who went to repair their Sandymount house could not cope with their eccentric habits and erratic moods and often decided to cut short their work at the house.

According to neighbours who got occasional glimpses inside, the home was filled with religious ornaments and pictures. Objects also seemed to be leaning near the front door.

The sisters regularly purchased masking tape from local stores and it is understood this was used to seal their windows. Some years ago a group of youths threw a rock at the house and broke a window over the front door. The Mulrooneys replaced the pane with paper.

This incident, and possibly others, appears to have propelled the Mulrooneys down a paranoid path for the rest of their lives. Along with religious observation (including almost daily trips to the church in Gardiner Street) and taking care of "mammy" (in fact their aunt Frances), this extreme defensiveness and suspicion of the outside world appears to have governed their every move.

Gardai from the local area remember being summoned one evening by the women to Tritonville Road. They complained a car had been outside and a man had been staring into the house for several days.

Gardai assured them the man was harmless. The few neighbours who did get a response at the door remember the time it took for the women to unlock the various heavy locks.

Other incidents stick in the memory of those familiar with them from Sandymount. Going out and cutting the grass with a scissors, painting rocks in the front garden, bringing home drums of paraffin oil in shopping trolleys.

While their behaviour was eccentric and puzzling to the wider community, those who came in contact with them say they were kind. The cats they kept in Sandymount were their devotion and stray birds were regularly rehabilitated at their home by Ruth and Catherine.

Frances was an important figure in her nieces' lives and they spent a lot of energy attending to her needs.

They would often talk to shopkeepers and had an almost Victorian air about them, remember neighbours. Nevertheless, Ruth immersed herself in the most up-to-date alternative medicine trends.

Before moving into the Sandymount area, the Mulrooneys had lived on the South Circular Road area of Dublin, where their parents owned a now defunct hardware store. Their parents lived above the shop. Their daughters and aunt Frances regularly worked there.

The sisters and Frances seemed to have enjoyed this period of their lives and the bond between the sisters appeared to be extremely strong, according to one man who remembers them in the store.

The death of their father many years later seems to have been a turning point and the sisters - who rarely mentioned their wider family, according to neighbours - recalled happy days helping him out with the store.

When they later bought items in Sandymount they were experts on the exact ingredients in paint and always wanted to know exactly how long paint would be on the wall before it started peeling. Anyone who struck up a conversation with them would have heard them talk about "Mammy" very soon into it.

When the news of the their deaths came this week, many people who knew them in Sandymount were surprised to hear that "Mammy" was Frances, their aunt. According to Mr Ryan, Frances seems to have reared the three sisters and was effectively their "mammy" for the last 20 years. No one is sure how this came about.

Mr Ryan - who also knew them when they visited a hardware wholesaler he worked in years ago - says in relation to any big decision they would always say, "we better talk to Mammy".

This protectiveness towards Frances in recent years seems to have fitted with their distrust and insecurity towards the outside world. Tables and chairs were used not just to block up doors for security reasons, but also so that Frances would not get cold.

One person familiar with the family said this week that Frances "ran the show" and her nieces looked up to her.

It is tragic that such devotion to Frances may have inadvertently contributed towards their death a week ago when they had the heating system on full power.

The departure from Tritonville Road, according to neighbours, was extremely traumatic for the four women. They had been renting the property but could not keep up with the rising rents in such an affluent area.

The changeable health of Frances, said neighbours, was causing them worry, and the disruptive move to Leixlip may have caused them to lose further faith in what they saw as hostile outside forces.

For the last few years of their lives they had little contact with their extended family and it is possible their close relationship sharpened their suspicious instincts.

The almost complete withdrawal from society appears to have worsened in Leixlip and their trust in the world beyond their blue front door seems to have declined sharply.

Their introspection and eccentricity were notable. Not only was the front door not opened and the curtains kept drawn in Leixlip, but now letters were not responded to, either.

In Sandymount, they had been enthusiastic gardeners, but in Leixlip, they allowed their garden become so overgrown and untidy that neighbours noticed.

Sources familiar with the four said two letters were sent by their health board in April asking them about their current status, but there was no response. While regular Mass attendance was part of their routine in Sandymount, worshipping seems to have been done behind the curtains in Leixlip, and local priests never saw them.

Frances was never left alone. If they went shopping, one of them would stay behind caring for her. They were never gone too long and according to neighbours they never went out at night.

Inside the house, the sisters seemed to be dependent on each other but their immediate neighbours never witnessed anything untoward. In fact, one neighbour claims they heard the sisters playing Joe Dolan music on one of the few evenings a window was opened.

While blocking up doors was a practice in Sandymount, it appears to have got so bad in Leixlip that the house effectively became air-tight. The obsession with security and fighting off draughts had made it a tomb.

About a week ago, according to Garda investigators, the sisters went to sleep in the front room. They were sleeping in a sealed house. A fridge was pressed against the front door, with a table and chairs behind it. Old newspapers and tape were used to seal any place where draughts might get in. One of the sisters was sleeping near a radiator on full blast. Unfortunately it was a radiator powered by gas-fired central heating.

No one knows what time the sisters or Frances went to bed that night. No doubt they went asleep believing all their determined taping and blocking would keep out intruders. But the terrifying irony was that danger lurked inside, unseen. In their rush to block out the world - even day-light - they had created conditions would would kill them.

The carbon monoxide crept up on them as they slept. According to medical sources they would have been asphyxiated over a period of hours.

Behind their drawn curtains they were falling into a deathly sleep, each breath diminishing the next. Nobody knew or could do anything; in fact some of the people in the houses around them did not know they were even there. As Liz Mulligan, who lives three doors down, said this week: "It is so sad they died there alone and no one knows them."

While the Leixlip neighbours have been criticised in some quarters this week for failing to perform the traditional Irish ritual of "looking out" for their neighbours, the sisters and Frances never showed any signs they wanted the outside world peeking into their closed environment.

What could anyone have done to draw them out of their shell? They were intelligent people and three of them were capable enough to decide their own lifestyle. As one neighbour put it this week: "We thought it was strange but you don't think of knocking and nosing into other people's lives."

For those clamouring for the return of the squinting windows, modern estates such as Rinawade Grove do not provide a test ground. Filled with young working couples busy in companies like 3Com and Intel, these estates have been created for work purposes, not for community purposes.

The fitting-out of houses in nearby Cyber Plains with Internet connections and other high-tech equipment is symbolic of this. Nevertheless. the ordinary heartfelt human gestures were enacted on the road this week and yesterday bouquets of flowers were lying on the porch of the women's house.