He is most critical to how a riot could turn out.
As such, the decisions made by the incident manager, usually the commander of a police division, are crucial.
A wrong assessment of the situation or deployment of forces could result in greater violence.
That was what Mr Khoo Boon Hui, senior deputy secretary for the Ministry of Home Affairs, told the Committee of Inquiry yesterday.
Mr Khoo, who was the Commissioner of Police between 1997 and 2010, appeared before the Committee yesterday and spoke about the riot control doctrine and measures here.
While he said that dealing with a mob is best left to the trained and equipped troopers from the Special Operations Command (SOC), the incident manager is responsible for managing the situation.
This is what Mr Khoo said the incident manager must do:
1. Assess the situation
What does the crowd want? Is the entire crowd passive or aggressive? Are there ringleaders?
These are questions that the incident manager will need to answer, said Mr Khoo.
It is not an easy role, given the incident manager will also need to give information to the police command, worry about the safety of his officers and decide on the most effective tactics based on available resources.
He is also the one who makes the request for reinforcements, if needed.
"The outcome depends on many considerations and these considerations require a very robust assessment," he said.
2. Contain the riot
Until the SOC arrives, the incident manager has to contain the rioters and ensure that it does not spread to other parts of the country, said Mr Khoo.
He also has to be careful not to escalate the level of violence without retaliation from the rioters.
Mr Khoo suggested using a loudhailer, siren or flashlights to engage the crowd.
"That is the most difficult time for the people on the ground - when you are waiting for reinforcements and you have to deal with the things that are going on," he said.
3. Use of force
There has been a lot of controversy regarding the best course of action, Mr Khoo said.
While the lack of or an ineffective amount of force could embolden the mob, excessive force could lead to greater violence, he said.
Committee chairman G. Pannir Selvam also said that firing a warning shot in a congested area could lead to rioters thinking that the police are firing at them.
But Mr Khoo said the incident manager ultimately must find a way to deal with the rioters.
"You can't just stand by and ... let the rioters escape. You have to bring people to justice."
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