An alert airport security officer who spotted a suspicious-looking couple decided to check on them. He then found that the pair, in their mid-30s, who were holding Bulgarian passports and headed for Paris, were Iraqis.

Corporal Arasu Kumaran, 28, was commended by Deputy Prime Minister S. Jayakumar at the National Security Seminar this morning to highlight the need for continued vigilance to keep Singapore safe and secure.

"The best policies or equipment are irrelevant if they are not executed by dedicated and well-trained people," said Professor Jayakumar, who is also the Coordinating Minister for National Security and Law Minister.

About 300 participants from government agencies and security associations are attending the seminar, which comes a day after the sixth anniversary of the terrorist attack on the New York World Trade Centre on Sept 11, 2001.

Urging everyone not to let their guard down, the minister said: "Since 9/11, many other countries experienced their own 9/11s - Madrid, London, Bali and Jakarta - and near 9/11s like the failed Jemaah Islamiah plot in Singapore."

The DPM also paid tribute to people on the frontline, like Corporal Arasu, immigration officer Savinder Singh, and Cisco officers Lee Chong Leng and Norazlee Abdul Ghani, for keeping Singapore safe.

Talking to reporters after the event, Cpl Arasu said that his suspicions were aroused by the couple's behaviour.

The 28-year-old Aetos security officer said: "They were watching my every move and appeared nervous. So when they showed me the Bulgarian passports, I asked where they came from."

As they could not understand English, Cpl Arasu found a Bulgarian woman who was also taking the same flight, to interpret for them - only to find out that the couple could not speak Bulgarian, even though they had Bulgarian passports.

The couple were turned over to the police.

The behaviour and body language of travellers are important clues, said the three other officers.

Immigration and profiling specialist officer Savinder, 45, has received more than 50 letters of recognition for nabbing immigration offenders and smugglers in his 24 years of service.

Corporals Lee, 31, and Norazlee, 26, were commended for stopping a worker smuggling 3kg of potassium silver cyanide through the Tuas Checkpoint in August.

The Malaysian had stolen the controlled substance from a chemical factory.