SPO2 Henry Elumbaring was shot from behind repeatedly as he was walking from his home just a short distance from the gates of the police camp to buy bread from a bakery.
His assailant fled into a nearby housing area, evading police who gave chase.
The attack came just a few days before a contingent of US troops was due to arrive in Sulu for joint exercises with government forces.
Elumbaring had played a key role in helping government forces track down members of the Abu Sayyaf, an extremist group linked by Washington and Manila to the al-Qaeda network.
Before he was slain, Elumbaring had provided security to foreign journalists who would cover the joint military exercises.
The Abu Sayyaf has carried out mass kidnappings and bombing attacks against Christians and foreigners over the past decade.
It has also killed about a dozen soldiers and civilians in Sulu since last year, despite a military crackdown.
The US State Department has tagged the Abu Sayyaf, or Bearer of the Sword, as a "foreign terrorist organization" and has put up millions of dollars in rewards for the capture of its leaders following the deaths of two US hostages at the hands of the Abu Sayyaf in 2002. — Roel Pareño, AFP