Police Ombudsman investigators have begun their probe into how the PSNI responded to the Greenvale Hotel disco crush tragedy on St Patrick's night.
On Tuesday, police admitted the first officers on the scene after the initial 999 call withdrew to await support and only moved in when the first ambulance arrived.
Chief Constable George Hamilton called in the ombudsman in order to establish the facts of the response feeling it in the public interest the actions of all those involved are considered. The families of the three teenagers killed have been informed of the development.
On Tuesday evening the Ombudsman's officer confirmed it had opened a case.
A spokesman for Dr Michael Maguire's officer added: "Our thoughts are with the families who have been so tragically bereaved.
“Our investigators have now begun gathering information about the initial sequence of events, and have appealed for witnesses to contact them. They are keen to hear from anyone who saw police in the area of the Greenvale Hotel on St Patrick’s evening, 17 March.
“Our investigators can be contacted by email at the following address: email@example.com.
“It would be helpful if anyone contacting us can include a contact telephone number in their email.”
Lauren Bullock (17) from Donaghmore, Morgan Barnard (17) and Connor Currie (16), both from Dungannon, died following the crush at the Greenvale Hotel as crowds of young people waited to gain entry to the venue on St Patrick's Day.
Greenvale Hotel owner Michael McElhatton and a 40-year-old man arrested on suspicion of manslaughter in connection with the incident have been released on police bail.
Deputy Chief Constable Stephen Martin said that the police investigation was "active and wide ranging" and "it is right and proper that the actions of all those involved are considered".
He revealed that the first police officers arrived at the hotel grounds shortly after receiving the 999 report.
Following their initial assessment they made attempts to establish more detail and information about what was happening and subsequently withdrew to await further police support.
When the first ambulance arrived police moved forward in support of them.
"The timing and nature of police actions during this period require further investigation to fully establish the facts," Deputy Chief Constable Martin said.
"The Chief Constable has therefore decided that the initial police response should be subject to independent scrutiny and it is in the public interest to refer the circumstances and the nature of the actions of the first officers arriving at the scene to the Police Ombudsman."
"The confidence of the families and the confidence of the communities we serve are at the forefront of our minds in our decision to refer this matter to the Police Ombudsman," Deputy Chief Constable Martin said.
"We will work with the Ombudsman to support whatever action he undertakes and would ask that people do not speculate or prejudge the outcome of the Ombudsman’s investigation."