Monday morning had started like any other day for veteran Channel Seven cameraman Greg Parker.

He was at work in the network's headquarters overlooking Martin Place, always a bustling pedestrian mall about 9.30am on a weekday, but even more so on this day, a week before Christmas.

Parker, who has covered major news stories around the world for the network, looks back now and remembers one of his producers walking back into the studio at that time, a "Lindt hot chocolate in hand".

Soon that name - Lindt - would consume his every thought and movement. For the next 16 hours, he and a police sniper did their best to monitor the movements of gunman Man Haron Monis, who was holding 17 hostages inside the popular Lindt Chocolat Cafe located directly opposite the Channel Seven building.

Within minutes of the triple-0 call being made to police about 9.45am on Monday, Parker had trained three cameras on the cafe, including one with a powerful 600-millimetre lens.

It allowed him to capture extraordinary, harrowing images of the hostages whose simple trip to a Sydney cafe on a Monday morning had landed them in very real danger.

"For me, one of the hardest things to see was ... three women forced to hold that flag up against the glass, and then another image of a poor guy in obvious distress with the muzzle of a shotgun in frame being pointed at his head," Parker said in an interview with Channel Seven.

"That was the first time we'd seen a clear threatening pose, that the gun was pointed at a bloke's head who was in a  very passive stance up against the glass."

Soon a police sniper recognised the unique vantage point of the Channel Seven headquarters, and moved in to take up position. The newsroom was evacuated - but the sniper quickly identified the potential value of Parker and his cameras.

"I knew we were getting something pretty remarkable in what we could see with our lens on the camera, and the sniper concurred and said 'Could we stay there and keep sweeping?' and giving him continual information of what we were seeing behind the glass [of the cafe window]," Parker said.

Channel Seven had initially been broadcasting live footage of the hostage drama, but cut that feed at the request of police. Instead, Parker fed those images back to police headquarters where senior officers were devising an action plan.

Soon those offices were asking Parker for specific camera shots.

"So we put on Kevlar vests and came down and relocated cameras as they needed them to be. Specifically, that window that they called 'Window 4', where the flag was being sort of held up, was where the gunman was continually positioning himself and putting hostages between himself and the window and between himself and the door," he said.

"It was genuinely horrible. In 20 years, it's very rare to come across such upsetting footage. There's nothing you can do.

"For a real long time it was just him [the sniper] and I, I think for five or six hours, making small talk and, you know, to be honest, the situation kept us pretty busy because we were both looking for any opportunity that was going to affect a positive outcome, and we continually were sort of blown away at just how sad the situation was. It went on and on. We both just were sort of praying that these people were going to get out."

When a group of hostages ran from the building late on Monday afternoon, Parker said he and the sniper were cheering, "high-fiving almost".

"But then the longer it went on, the lights [in the cafe] went off, you know, signs weren't looking good and the scene was getting worse by the hour."

As the hours went by, Monis' actions became more erratic, Parker said. He became agitated, was shoving the hostages, and using them as a shield between himself and the windows.

When a single gunshot rang out just after 2am on Tuesday, police quickly sprang into action, he said.

"We heard a shot, he [the sniper] confirmed 'Hostage down, window two'. Six seconds later, we saw the special forces guys breach. It was ... pretty loud, pretty frightening, it's like nothing I've ever seen before, ever.

"The moment he [Monis] crossed the line, of taking down a hostage, it was a forced action from police. They, in my mind, and probably in anyone else's seeing it, I don't think they were going to sit around and wait for another hostage to have the same fate."

Parker said the "look of just anguish" on the faces of the hostages would live with him forever, as would the courage and professionalism of the police who carried out the dangerous operation.

The tragedy would not dim his love for the city he had grown up in, he said.

"I love Sydney, born and bred. I don't think anyone will let the lunatic that we saw harm our way of life. It's a beautiful city," he said.

"To me it's the best country in the world and always will be."