Books of condolence have been opened across Co Tyrone in memory of three young people who died in a crowd surge on Sunday night.
CCTV footage is being examined after teenagers were caught in a crush outside a disco in Cookstown.
The PSNI has asked parents to talk to their children about what has happened.
President Michael D Higgins says it was a 'terrible loss of life on St Patrick's Day' - and he's offered his condolences to the friends and families of the victims.
Catherine McHugh, principal of the college where one of the teens who was killed, Lauren Bullock, attended said the pupils have taken part in a prayer service to remember her.
"Our young people came in, lots of Lauren's friends, and we gathered together with our sister school next door, St Patrick's Academy and had a joint prayer service with pupils, parents and staff," she said.
Cheerleader Lauren Bullock, 17, keen sportsman Connor Currie, 16, and Morgan Barnard, 17, from Dungannon in Co Tyrone, died after a crush outside a St Patrick's Day disco in Co Tyrone.
Police said it appeared that people had fallen and then been fatally injured, but are still investigating the cause.
