Sydney siege: Negotiator - Establish rapport, keep control

A police officer runs along a street close to the cafe under siege in Sydney's central business district. Photo / AP

One or two words can be enough to turn a hostage situation, so language and rapport is everything, a former New Zealand hostage negotiator says.

"The first thing is to establish communication. The second thing is to establish a rapport with the person or persons and then just to try and calm the situation down and keep it all very controlled," said Lance Burdett, former national adviser for the New Zealand police negotiation teams.

"It's about getting the information as to what they want and why."

Mr Burdett, who worked in police hostage negotiation for 13 years and co-ordinated the negotiations for the Napier siege in 2009, said being open-minded and remaining calm was key.

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"There's a lot of assumptions going on and the worst thing you can do is close your mind.

"It's very difficult, you don't want to go direct, particularly in the beginning. You're in the most dangerous time at the beginning of these negotiations and then obviously at the end," he said.

Checking whether everyone was okay was one of the first questions.

"You've got to make sure no one is injured, and you ask that question - are you okay, and then is everyone else in there okay," Mr Burdett said.

"You've got to basically get that rapport going. Keep them talking there as long as you can for as much as you can."

Passive language was used and "aggressive words" like gun, bullet, and violence were avoided.