The Police Ombudsman's Office has found that police failed to properly investigate the disappearance of 15-year-old Arlene Arkinson from Castlederg in County Tyrone in 1994.
Arlene was last seen in the early hours of August 14, 1994 in the company of a man who had given her and two other people a lift home from a night out. The man said Arlene got out of the car shortly after he had left the two others off.
The man was arrested but was later released without charge. Following further investigation, he was re- arrested in 2002 and charged with her murder. He was found Not Guilty following a trial at Belfast Crown Court in 2005.
The reason for Arlene's disappearance remains unresolved. Police now believe she has been murdered, although her body remains undiscovered.
The man who was last seen with Arlene was subsequently arrested, tried and convicted of the murder of 14-year-old schoolgirl Hannah Williams in Kent in 2001.
A member of Arlene Arkinson's family made a number of allegations to the Police Ombudsman's Office that police had failed to effectively investigate her disappearance.
The Police Ombudsman found that police did conduct quite a thorough initial investigation, focusing on Arlene's last known movements. The investigating officer correctly identified areas for searches, spoke to key witnesses and quickly identified inaccuracies in their accounts.
However, a spokesman said there is no record that police searched Arlene's home during the first 48 hours of the investigation.
CID did not respond with vigour to reports that a vulnerable person was missing, having last been seen in the company of a man who was a known sex offender
"Although Arlene had previously stayed away from home overnight, she had never before been reported missing to the police. The officers who initially dealt with this case quickly identified concerns and reported them to CID. The CID did not respond with vigour to reports that a vulnerable person was missing, having last been seen in the company of a man who was a known sex offender. Together these aspects should have alerted them sooner to the possibility they were dealing with a potential murder enquiry. They should have conducted their investigations accordingly, until this proved not to be the case," he said.
The Police Ombudsman's Office also substantiated a complaint that police should have arrested this man sooner.
"Key police officers when interviewed said they initially treated the investigation as a missing person inquiry rather than a possible abduction/murder.
Police had grounds to arrest a man within 48 hours, but did not arrest him until 46 days later.
"However the grounds to arrest this man were available within 48 hours of Arlene being reported missing. His statement to the missing person inquiry included a number of inconsistencies; he was on bail for serious sexual offences and had been convicted of a number of sexual crimes. These factors should have raised serious concerns for the whereabouts of Arlene.
"The police did not arrest him until 46 days after the disappearance was reported. The failure to do so sooner prevented the seizure of clothing he wore on the night of the disappearance and allowed for the opportunity to dispose of evidence. The early seizure and examination of significant exhibits would have had the potential to provide valuable evidence," said the spokesman.
The Arkinson family also asked what material existed in 2002 which allowed a man to be charged with the murder which did not exist when he was first arrested.
In cases such as this, police were required to prepare and submit a file to the Director of Public Prosecutions, who would decide on whether or not a prosecution was justified.
The 2002 phase of the investigation used 'similar fact' evidence in the presentation of evidence to the Director of Public Prosecutions. This included the evidence of a witness who had come forward in 1993 and the similarities with the murder of Ms Hannah Williams.
The 1994 phase of the investigation did not have the knowledge of the murder of Ms Williams. Without this material, and with the denial of the suspect, a decision was made that there was insufficient evidence to charge the suspect with the murder," said a spokesman.
Ultimately, however, the similar fact evidence was not presented at court, but this was a decision taken by the DPP rather than the police.
The Police Ombudsman rejected an allegation that police failed to take action in relation to a suspect's breach of bail. He also said police had reasonable grounds to arrest and interview a man who was subsequently eliminated from their enquiries.