Detectives have appealed for patience on the first anniversary of a St Patrick's Day tragedy in which three schoolchildren from Northern Ireland died.
Three teenagers were killed in a crush as they waited to gain entry to the St Patrick's Day disco at the Greenvale Hotel in Cookstown.
Lauren Bullock (17) died along with Morgan Barnard (17) and 16-year-old Connor Currie - all from nearby Dungannon, Co Tyrone - died outside the venue, which was being attended by hundreds of young people.
Detective Chief Inspector Eamonn Corrigan said: "One year on from the heartbreaking events, our thoughts remain very much with the families of the three teenagers who sadly lost their lives at the St Patrick's night event, and also with their friends, anyone who witnessed the tragedy unfold and the wider community.
"We do not underestimate that today will be extremely painful and traumatic for the families of Morgan Barnard, Lauren Bullock and Connor Currie and I would like to reassure them that our focus remains firmly on trying to find answers for them.
"We remain in close, regular contact with these families providing them with updates on the progress of the investigation, which is one of the largest undertaken by the PSNI. We will continue to offer them personal updates at any time of their choosing."
Mr Corrigan asked for patience from the families due to the sheer volume of evidence involved.
"However, we remain absolutely committed to building up an accurate picture of what happened last St Patrick's night," he said.
He said this involved over 1,000 witnesses, including around 800 young people who were there that night.
"It takes time to cross-reference witness statements with CCTV footage, mobile phone videos and phone calls made to the emergency services as well as other evidence gathered. I understand the length of time this takes can be frustrating for the teenagers' loved ones but it is important we get this right for them."
To date, a total of 148 people have been identified as potential significant witnesses where it was deemed appropriate to carry out in-depth video interviews. Analysing the interviews and identifying the relevant evidence forms a major part of the investigation.
In addition, 207 written witness statements have been taken from young people at the venue that evening.
Police have spoken to a further 400 young people who either declined or were deemed unnecessary to record a statement.
Two people have been arrested so far and have since been released pending a report to the Public Prosecution Service.
A further eight men - at the time aged 26, 26, 27, 27, 36, 39, 50 and 53 - were interviewed under caution.
Seven of the men have been further interviewed under caution and will be subject to a report to the PPS.