But they declined to comment further on the specifics of the shooting, which happened in front of scores of passengers at the Outram Park MRT station.
In the past, officers have said the weapons, which can deliver a 50,000-volt shock, were never meant to replace conventional guns in life-and-death situations.
Since the shooting, talk on the Internet and calls to The Straits Times news hotline have centred on whether police needed to kill Lim Bock Song.
Police said Lim, the prime suspect in a murder half an hour earlier, brandished a 20cm-long knife and lunged at two officers.
Central Police Division commander Lau Peet Meng said on Thursday that the officer had 'no choice' because Lim was a murder suspect.
'The armed and dangerous suspect approached my officers in a threatening manner at close proximity,' said Superintendent Lau.
Dr Teo Ho Pin, who chairs the Government Parliamentary Committee for Home Affairs and Law, yesterday backed the decision to open fire.
'The situation was so tight that the officer could not even fire a warning shot, so he had no choice but to bring down the assailant,' Dr Teo said.
Stun guns were first deployed here by police in 2005 and have since become standard issue for frontline officers.
The weapons - placed on the officers' belts - work by shooting out two barbed darts. They hook onto the suspect's clothes or skin and send a 50,000-volt electric current through the body for five seconds, temporarily incapacitating the target.
Some former police officers, like 62-year-old security manager Cyril Sta Maria, said only the policemen involved in Thursday's shooting were in a position to judge which weapon to use.
CAROLYN QUEK & DIANA OTHMAN