The families of Tori Johnson and Katrina Dawson have spoken for the first time of their anger at police tactics on the day of the Sydney siege.

Speaking exclusively to Four Corners, they said they were devastated to hear during the inquest that police had only planned to go into the Lindt Cafe if gunman Man Haron Monis killed or seriously injured a hostage.

"I can't forgive people for that trigger," said Rosie Connellan, Tori's mother.

"I'll never be able understand how you can make a calculated decision that you wait for someone to die. It's just beyond me."

Tori Johnson's family has been a constant presence at the coronial inquest since it began in May 2015.

Rosie Connellan comforts Thomas Zinn during the filming of Four Corners interviews. ( Four Corners: Justin Stevens )

The decision by police to storm the cafe came only after Tori was shot and killed by Monis.

In the preceding minutes, Monis had forced Tori at gunpoint to kneel in front of him.

At the start of the inquest, Ms Connellan believed the role of police in the events leading to her son's death was straightforward.

"We thought that Monis had killed Tori and it was relatively simple: the police had done everything possible and that was it," she said.

Tori Johnson was the manager at the Lindt Cafe in Martin Place. ( Supplied )

But the evidence that emerged at the inquest proved shocking for the families.

"As it unfolded it was just, it was horrific. Every day we thought: 'This can't get worse', and every day it got worse — what was coming out in evidence," Ms Connellan said.

Listening to multiple accounts of her son's execution by Monis was harrowing.

"Every time they reached that last 10 minutes, I had the same physical reactions and I was just so aware of the fact that Tori was still alive at that moment — it was almost like I was stepping back in time to that night every single day of the inquest listening to that," she said.

Tori's partner of 14 years, Thomas Zinn, said he had lost faith in the police.

"I have no trust because of the great level of incompetence that has been revealed," Mr Zinn said.

Sorry, this video has expired The families of Katrina Dawson and Tori Johnson speak to Four Corners

The family of barrister Katrina Dawson, who was killed by police gunfire when officers stormed the Lindt Cafe, attended the 18 months of inquest hearings to understand how she died.

"From the very beginning we decided that we had to go each day, that there had to be a human element injected into this," Katrina's mother Jane Dawson said.

"I think the Johnsons probably felt the same way, but we felt very strongly that Katrina should be represented and it was up to us to make sure of it."

Katrina Dawson worked as a barrister near the Lindt Cafe. ( Supplied )

Katrina's parents told Four Corners of the distress of listening to the details from police at the inquest.

"What I said in the beginning was that we weren't after retribution. But what we did want desperately was for them to have the courage to tell the truth," Mrs Dawson said.

"To admit the mistakes and then talk about what they would do to rectify those mistakes," Katrina's father Sandy Dawson said.

"But we never saw anything like that."

The families hope the coroner's recommendations will bring about significant change.

"I want to see the coroner have the courage to really challenge an alternative view of what could have happened and to make sure the lessons are being learnt and that it honours the remarkable memories of Katrina and of Tori," Katrina's brother Angus Dawson said.

But for both families, there remains a lasting mistrust.

"If there is no recognition in the authorities that mistakes were made and that these failures have happened, then this learning will never occur and this culture will not change," Mr Zinn said.

"I think we all had this feeling that the police are there to protect us all and that they know what they're doing — that's one of the worst things about this is that we feel very let down," Mrs Dawson said.

Watch The Siege: Part 1, a Four Corners special investigation, tonight at 8:30pm on ABCTV and ABC iview. The Siege: Part 2 will air Monday, May 29, 2017 at 8:30pm.