Lawyer John Bamford broke his silence to reveal he was the city worker dubbed "chair man" who approached 20-year-old Mert Ney before his arrest on Tuesday.

Ney is accused of killing 24-year-old Michaela Dunn in a Clarence Street apartment before allegedly stabbing 41-year old Linda Bo at the Hotel CBD. He's yet to be charged.

Mr Bamford on Thursday said he was getting lunch when he saw a man emerge from the side of a building with a "knife raised".

"I just grabbed the chair and, you know, went after him basically as best I could," he told Seven's Sunrise.

"I had to get rid of my papers that I had taken for lunch to read so I had to drop them on my cafe, but the guy knows me there so I didn't worry about that."

Mr Bamford said he had no option but to act and the public's reaction to his bravery was "a bit over-egged".

"What am I gonna do, go home and say I was there and I could have done something and backed away from it? I mean there was just, there was no option," Mr Bamford said.

The lawyer also revealed he had a "little chat" with Ney. He said the 20-year-old claimed he had a bomb in his bag.

"(But) the zip was undone and it didn't look like there was a bomb in there to me. He was just having me on."

NSW Police Commissioner Mick Fuller has described the men who helped detain Ney as "the highest order of heroes".

"They saved lives," he said.

Australian Associated Press