As police made the critical call to storm the Lindt cafe after gunman Man Haron Monis executed hostage Tori Johnson, their radios failed, an inquest has heard.
As soon as snipers reported Mr Johnson had been shot dead, with the words "hostage down" ringing out over the airwaves, the commander of the crack Tactical Operations Unit attempted to activate the emergency action trigger required for his men to enter the building.
"Echo Alpha this is Tango Charlie - commit the EA," he broadcast over the police radio network.
There was no movement at the front line nor confirmation over the airwaves.
As he tried to broadcast the message again seconds later, his deputy, who was standing beside him at the forward command post, intervened.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"I stopped him and said, 'No, let me' in case his radio wasn't working a second time ... I took the initiative to make the call," the former senior Tactical Operations Unit member told an inquest into the stand-off.
Because there had already been a delay, he shortened the command and also fast-tracked the authorisation process.
"All teams commit the EA," he broadcast, before repeating the code word three times.
Heavily armed officers then stormed the cafe at 2.13am on December 16, 2014, shooting Monis dead more than 17 hours after the siege began.
Another hostage, Katrina Dawson, was also killed after being hit by police bullet fragments.
Problems with the radio system also prevented anyone from receiving reports that Monis had fired a second shot at 2.09am, the former officer confirmed.
Monis fired the first shot at 2.03am as six hostages escaped, shattering the glass above their heads and rupturing what looked like a sprinkler or fire extinguisher.
The forward command post was never told that Mr Johnson had been seen on his knees at 2.06am because of the radio issues.
The ex-officer told the inquest that police snipers should have kept trying to broadcast their reports using radios and mobile phones.
Police could go days without encountering any radio problems but when the network did falter, it would break down two or three times in one day, the deputy tactical commander said.
"Murphy's Law is that it always happens at a critical time," he said.
Earlier on Monday, the ex-officer said he feared that Monis' first gunshot could have been a tactic to lure police inside the cafe before detonating a bomb.
He said the possibility Monis was carrying an improvised explosive device represented a "huge, unquantifiable risk".
However, he said had one of the escaping hostages been injured in the gunfire, an emergency action would have been triggered regardless of the threat of the IED, sending officers into the building.
The inquest is set to resume on Tuesday.
