Supporters who helped the Omagh bombers avoid capture were tonight urged to break their silence and help police put them behind bars.
As the fourth anniversary of the atrocity loomed, the detective heading the hunt said he shared the frustration of victims' relatives at the lack of progress.
Superintendent Norman Baxter vowed to do all in his power to catch the Real IRA unit who murdered 29 people in the Co Tyrone town on August 15th, 1998.
But police were powerless to act without vital information. He said: "The Omagh bombers would have relied on a network of supporters to provide transport, acquire equipment, provide safe houses and wash clothes to destroy evidence.
"These people should examine their conscience.
"Someone out their must have the information that will help the police bring to justice the perpetrators of one of the worst atrocities ever committed in Northern Ireland."
No one has been convicted of carrying out what was the worst single act of terrorism of the Troubles.
One man was jailed for aiding the bomb gang through lending them mobile phones to use on the day of the attack.
PA