David Lawler did not fit the profile of a murderer. The long-haired, bearded telephone technician had a steady job, a wife and a six year old son. One of five children, he joined Telecom Eireann as a bright school-leaver from Baltinglass, Co Wicklow. He worked installing phone and computer modem lines and was a keen Internet user.
In Blanchardstown they nick named him "Jesus Christ" and "God" because of his hair and beard. When gardai took a blood sample to check his DNA he looked up DNA on the Net for information on how likely it was that they could make a match.
"He just looked it up, found out whatever information he had on it and kept it to himself," a senior garda involved in the investigation said.
Lawler had no criminal record. There was no history of violence and his family background was described as stable. On Friday, December 22nd, 1995, then aged 31, he committed that most frightening and unusual of murders - a random attack on a woman he simply met on a dark path.
Both murderer and victim were on their way home from their office Christmas parties. Lawler had been at his party in the Exchequer Hotel in Dublin city centre since lunchtime the previous day.
It was sometime after 3.30 a.m., after more than 12 hours' drinking, when he was walking to Edgewood Lawn in Blanchardstown. He told gardai he could not get a taxi so he walked from town.
Marilyn Rynn was also returning home from her office party. She had left the Shieling Hotel in Raheny alone at around 2 a.m.
She took a taxi to the city centre and met some work friends in Eddie Rockets diner on O'Connell Street. At around 3 a.m. she went to Westmoreland Street to get the Nitelink bus home.
She had enough money - her week's wages - in her handbag to get a taxi, but it would have been more than an hour's wait in the Christmas rush. She was used to getting the Nitelink, and taking the short-cut home along the Tolka Valley Park.
As she walked down the path and tunnels from the bus stop to her home, Lawler came walking behind her. He had never met her before. Both were minutes from their homes.
She lived alone. His wife and six-year-old son were waiting for him.
He said he just did it on spontaneous impulse. Sometime before 5 a.m. he raped Marilyn Rynn and strangled her with his hands, leaving her naked body in brambles, her clothes and handbag nearby.
Yesterday he pleaded guilty to her murder and received a life sentence. His wife, parents, two brothers and a sister were in court.
Ms Rynn's elderly parents, her brother and sister were also there.
After the murder and before he was arrested and charged in August 1996, his wife conceived a second child. Gardai said she never knew, until her husband was arrested and charged, that he had murdered and raped Marilyn Rynn near their home.
Ms Rynn's body was found by a Garda dog less than 15 minutes into the first search of Tolka Valley Park on January 6th.
It had been more than two weeks since the murder and gardai said they had been hampered by false sightings since her disappearance and by her friends being away from Dublin over Christmas.
The investigation that followed was a vast trawl through suspect lists. Gardai took more than 2,000 statements and 354 blood samples for DNA testing. Almost 100 samples were taken from men with a history of sexual assault.
Many of the samples had to be sent to Belfast for analysis, as the facilities were not available in Dublin.
Lawler was first questioned almost immediately after the body was found. Answering house-to-house inquiries, he admitted to gardai that he had been in the area that night. In February 1996 he gave a blood sample voluntarily to gardai.
There was speculation yesterday that Lawler believed the delay between the murder and the body being found would mean that a DNA link would be impossible to make. However, a senior garda source said Lawler gave blood with the attitude that he would "run the gauntlet to see what we had."
In July 1996 the first test results came back indicating that Lawler matched the DNA profile of the rapist. Further tests were taken and he was arrested and charged with the murder on August 6th.
He was released on bail on condition that he lived with his parents in Baltinglass, Co Wicklow and sign on daily at the local Garda station.
Marilyn Rynn was described by a garda close to the case as being close to her family and having a wide circle of good friends.
Less than three days before she was murdered, she had celebrated her 41st birthday with a quiet get-together with her brother Stephen and his wife. They lived just around the corner from her meticulously-maintained house at Brookhaven.
She had many friends among her colleagues in the Central Statistics Office and the Department of the Environment, where she was an executive officer.
An independent, professional woman, she enjoyed aerobics and keep-fit classes, pottery and gardening, and socialising with girlfriends. She walked the shortcut through the Tolka Valley routinely day and night.
The investigation into her murder never lost momentum, according to a Garda source, and the incident room was still receiving huge numbers of calls when Lawler was arrested and charged.
There was "something about this murder" that touched many people, the source said. There were hundreds of calls after an appeal on Crimeline for information on any men who might have been scratched or bruised.
Lawler did not have any marks of a struggle with his victim. At first he was dealt with like any other suspect - questioned so that he could be eliminated.
Yesterday Ms Rynn's family was told that she had been simply very unlucky to be where she was that night.
After her daughter's murder Mrs Christine Rynn said Marilyn had a "happy life. She couldn't have asked for better."