Shane Clancy took the knife that he had bought less than an hour before and wedged it into the grass in the small back garden. He was covered in the blood of three people and had decided that there was only one way out.

He took a step backwards and judged the distance between the middle of his chest and the razor-sharp blade that was just about visible against the light created from the kitchen of the semi-detached house in the Bray estate.

The 22-year-old put his hands behind his back and let himself drop forward, the knife piercing deep into his heart. Although he died instantly it would be several hours before his body would be found.

It was just one bizarre moment in a horrifying murder-suicide that has shocked and captivated the nation in equal measure.

In the space of little over 10 minutes in the early hours of last Sunday morning, Sebastian Creane lay dead in the bedroom of his family home after being knifed through the heart. By his side was his older brother Dylan, unconscious after suffering eight stab wounds and a punctured lung when he went to investigate the sound of screams in the house. Just yards away Jennifer Hannigan was being comforted after summoning the strength to escape through a window of the Creane house and knock on a neighbour's door and beg for help. The blade of a knife had snapped from its handle and was wedged in her back.

Gardaí and the emergency services arrived within minutes and the scene that greeted them was one that is normally associated with horror films, not a solidly middle-class area in a leafy corner of Co Wicklow.

One week after Shane Clancy went on the rampage before taking his own life there are more questions than answers about what motivated him.

Much of the rumour, speculation and confusion has arisen because the media – eager to splash the story on their front pages – have leapt on stories that are half true, at best the truth of what has happened in the house in Cuala Grove has been distorted by sensationalism.

Gardaí have established the timeframe of events last Saturday night and Sunday morning.

Twenty-two-year-old Seb Creane's night started off the way many young people begin their weekends. He arranged to meet two friends he had gone to secondary school with for a couple of pints.

The three began drinking in the Eagle House in Sandycove where they had no more than two or three drinks each. They had arranged to meet a female pal in the Queen's pub in Dalkey and when they arrived after 10pm the woman was there along with four or five of her friends.

Among that group was Shane Clancy, who was due to begin the final year of a four-year course in Irish and theology studies at Trinity College. Clancy was due to spend this summer abroad but cancelled his plans at the last minute and was working in a nightclub until he went back to college.

Creane and Clancy were on nodding terms and knew each other through their mutual friend. They had met several times before. They were neither friends nor enemies. Gardaí say they had a cordial relationship.

Five months previously, Clancy had ended a three-year relationship with his girlfriend Jennifer Hannigan, but like many young people he had regretted this decision and had tried to patch things up with her.

Hannigan didn't want to get back together though and was trying to move on with her life. She was going into fourth year of a degree in visual communications in the Dun Laoghaire Institute of Art, Design and Technology. One of her classmates was Seb Creane. The pair had been friendly in college, but had only recently started to see each other casually.

Less than three weeks before they had decided to go out and were in the very early stages of a relationship which sources say was not overly serious and was in the 'let's see how things go' category.

Clancy did not take Hannigan's rejection well. He had been prescribed anti-depressant medication which he had begun taking a week before carrying out the murder. Garda sources say that he might have been using more than the recommended dosage, but will not know for sure until they receive toxicology reports over the coming weeks.

On good terms

Even though Hannigan did not want a relationship with Clancy they were on relatively good terms. Gardaí say there is absolutely no evidence to suggest that he was stalking her or had contacted her friends through social-networking sites.

After spending several hours in the pub in Dalkey the group headed to the Vico nightclub in the town. Clancy was on a night off, and because he did not drink he drove to the pub.

At around 3am the group came out of the club. Clancy offered to drop Creane and his two friends back to Bray. The group had only a moderate amount of alcohol taken. They were not drunk and were in good spirits.

Creane's two friends have been interviewed by gardaí and say that they exchanged general chitchat on the journey home. Creane and Clancy were getting on well and not a bad word was spoken between them prior to the two friends getting out of the car.

It is pure speculation about what occurred when the two men were alone in the car. It is likely that Clancy was not aware that Creane had recently started to see his ex. Gardaí say it is possible that it came up in conversation, which may have driven Clancy over the edge. However, detectives are keen to point out that they do not believe that the murder was planned and do not suspect that Clancy set out to drive Creane home with the intention of killing him.

Seb Creane got back to his house after 3.30am. Jennifer Hannigan arrived soon afterwards, as arranged earlier. Creane's parents were on holidays abroad.

His brother, Dylan, a 28-year-old who ran a web-development company from the family home, was in bed asleep with his girlfriend Laura Mackey, who is a guitarist with the rock band Boss Volenti.

As far as Seb Creane was concerned, everything was normal. Little did he know that something had driven Shane Clancy over the edge.

Whether Clancy waited outside the house in his car and saw Hannigan arrive is not known, but he drove to the 24-hour Dunnes Stores in nearby Cornelscourt and paid around €7 for what is believed to have been a set of up to three knives.

After returning to Bray at around 4.30am, he took one of the kitchen knives from its hard plastic packet and gained entry to the Creane house. It is probable that he knocked at the door and barged his way in when it was answered.

A row developed downstairs, which led Clancy to produce the knife and chase Seb Creane up the stairs into his bedroom. Clancy stabbed his victim several times in the chest, fatally wounding him.

Clancy then turned his attention to Hannigan. He punched her in the face and head before stabbing her in the back with such force and hatred that the knife broke and lodged in her back.

Hannigan bravely managed to escape through a window and staggered to a neighbour's house for help. She is recovering well and has spoken to gardaí. They say she has been "incredibly helpful" but do not want to go into details of what she has told them.

With the knife that he had bought broken, Clancy went downstairs to the kitchen and took another sharp knife from a block that was on open view. At this stage Dylan Creane was awake after hearing screaming and rushed in to help his brother.

He was also attacked. He lost a frightening amount of blood and was lucky to survive. He is still in a serious condition in hospital but is expected to survive.

Gardaí and three ambulances arrived just after 5am, but Clancy was nowhere to be found.

A murder inquiry and a massive manhunt for the escaped killer were immediately launched but gardaí didn't know that Clancy was lying dead in the garden because they had sealed off the property for a forensic examination.

Single stab wound to the heart

When a murder has taken place it is standard garda procedure to 'preserve and protect' the area and then 'secure and isolate' the scene – it was not until mid morning that Clancy's body was discovered by members of the Garda Technical Bureau. He had suffered a single stab wound to the heart and it was obvious that his death had been a suicide.

Gardaí do not believe that Clancy was under the influence of illegal drugs. The main theory being investigated is that he was misusing his anti-depression medication. Detectives say the medication may have triggered a reaction, leading him to lose control and snap.

When a tragedy like this happens it is easier to understand when the perpetrator has a history of violence or mental illness and has shown signs that they are capable of extreme violence.

Nobody saw this coming with Clancy though, and gardaí have yet to interview anybody who has spoken about him ever showing a propensity towards violence or aggression. People who knew Shane Clancy say he was an ordinary, decent person who didn't drink, smoke or do drugs.

At his funeral last Thursday at the Church of the Assumption in Dalkey, Fr John McDonagh spoke of a young man admired by all those who knew him, a man who had donated his 21st birthday money to charity and who had a bright future ahead of him. The depiction was a million miles away from the individual of last Sunday morning.

The priest said that "the Shane that many of you knew and loved was overtaken by a cruel darkness early on Sunday last, bringing great tragedy to two other families as well as his own".

He added that the dead man was in a "psychotic state and destructive frenzy".

Clancy's mother Leonie, father Patrick, stepfather Tony and four brothers and two sisters all attended the burial and are said to be deeply traumatised. The family are from Dalkey and were said to have been very close to Shane.

Seb Creane was also a man with a bright future ahead of him. He was a keen photographer who set up an account on the Flickr website to show off his photographic skills.

Conscientious and diligent

Tom Geraghty, the headmaster of the exclusive St Gerard's school in Bray where Creane attended, paid tribute to his former pupil, saying: "The staff of the school remember Sebastian as a hard-working, conscientious and diligent pupil who was consistently popular with both pupils and teachers of the class of 2005. Sebastian was always the perfect gentleman who cheerfully and willingly gave of his best in all school activities."

He was also a talented Gaelic footballer who played with local club Bray Emmets for a number of years.

The musician Phil Coulter led the flurry of tributes on Liveline, which has given the case almost blanket coverage. Coulter has been very visible talking about his son's friendship with Seb Creane.

The murder-suicide investigation is being led by detective inspector Frank Keenaghan, an experienced and respected officer who has been in constant touch with the families of Seb and Dylan Creane, Shane Clancy and Jennifer Hannigan. He pointed out that what happened was a tragedy for all three of the families.

Sebastian's parents, Jim and Nuala, were in the UK at the time of the attack and rushed back to Ireland when gardaí informed them of what happened.

The grim task of contacting them fell to Keenaghan.

He said: "The Creanes came home very quickly. It was a tough, tough, very difficult situation. It was one of the more difficult things you have to do in the line of duty."

They have not returned to the house since last week and are being comforted by family and friends. Nuala Creane is a teacher whose specialist area is in people with learning disabilities. She has her own training consultancy business which she operates from her own home.

Neighbours of the Creanes are shocked about the horror that visited their doorsteps and have refused to talk to the media. The only visible tribute to the dead man is a lone wreath that has been placed at the gate of the house.

Local parish priest Fr Larry White said he expected the Creanes to stay away from their home for the foreseeable future, "if they can ever return there".

The garda investigation is ongoing but there is very little that it can achieve. It is a fact that Clancy murdered Creane and then killed himself and that is what the probe will find.

As for the reasons that drove Shane Clancy to do what he did, the only two people who can probably explain it are dead.

All that is left is speculation and supposition along with two sets of parents who have both lost sons and a young woman who will somehow have to try to put the heartbreaking events of a week ago behind her and attempt to rebuild her shattered life.