KUALA LUMPUR: Nothing2Hide was meant to be a civilised dialogue between the Prime Minister and non-governmental organisations on issues of the day, including 1MDB.
But when chaos erupted an hour before the forum was scheduled to start, the police called it off, citing security concerns.
More than 2,000 people had turned up at the Putra World Trade Centre to see Datuk Seri Najib Tun Razak and Tun Dr Mahathir Mohamad.
Expectations were high because the people wanted to see both Najib and Dr Mahathir, the Prime Minister's most vocal critic, at the same venue.
Najib had confirmed his attendance on Thursday while Dr Mahathir, whom the organiser SukaGuam, a legal aid group, said was not officially invited, turned up at about 8.45am.
However, Inspector-General of Police Tan Sri Khalid Abu Bakar tweeted at 8.53am that the police had ordered that event be cancelled.
Many in the audience were heard condemning the decision.
The situation quickly turned ugly with fist fights and attempts by latecomers to cram into the already packed hall.
At 10.15am, it was announced that the organisers were still trying to negotiate with the police to allow the event to go on.
The organisers, the police and several other parties met Dr Mahathir to inform him of the cancellation and that Najib had been advised not to attend, but a source said the former prime minister insisted that he be allowed to speak to the audience.
Minutes later, Dr Mahathir made his way into Dewan Tun Hussein Onn and went on stage to talk about his unhappiness on what he said were serious irregularities in 1MDB.
Six minutes into his speech, Dang Wangi OCPD Asst Comm Zainol Samah approached Dr Mahathir on stage and asked him to stop speaking.
The audio system and the big screen monitors were shut off, angering the audience further as they demanded that Dr Mahathir be allowed to finish his speech.
Policemen, armed with sub-machine guns, entered the hall to keep the crowd from getting out of control.
Police allowed Dr Mahathir to hold a press conference later.
"I'm just an ordinary man. I don't have guns or mean any harm to anybody. Why should people be afraid of me?" he asked.
Asked if he felt that Najib had instructed the police to stop him from speaking, Dr Mahathir said: "I don't know if he instructed. Police came up to me when I was talking and told me to stop. So I stopped because I am a very obedient citizen."
During his speech, the former prime minister said although Najib's father Tun Abdul Razak Hussein was his idol and that he was grateful to him for being able to get the country's top job, he had no choice but to go against his son.
"I wanted Najib to continue Tun Razak's struggle but I found many of his policies do not bring benefit to our country," he said, adding that the last straw was the alleged "loss" of billions of ringgit by 1MDB.
Dr Mahathir said he wanted to turn up at the dialogue so that he could listen to the Prime Minister's explanations.
"If his explanations were good, I would have resumed my support for him but since he did not come and explain, I will not support him," he said.
Dr Mahathir said Najib's no-show meant that he had lost the opportunity to win over support for himself and explain "everything and that no money is missing".
A crowd of supporters who followed Dr Mahathir as he was led out of the hall was heard shouting "Long Live Tun Mahathir, where is Najib? He is hiding."