PC Sharon Beshenivsky was shot along with fellow officer PC Teresa Milburn when they were called to a robbery at a travel agents in Bradford in 2005.
Since then, six men have been jailed in connection with her murder.
However, police say a seventh man - Piran Dhitta Khan - allegedly fled to Pakistan following the attack and the investigation is going.
PC Milburn was also wounded during the shooting.
Detectives have renewed an appeal for his whereabouts, offering a cash reward for information leading to his capture.
The appeal comes as friends, family and colleagues from the force gathered to remember the popular PC at her annual memorial service in Bradford city centre today.
Detective Superintendant Simon Atkinson, from West Yorkshire Police, said: “This investigation remains ongoing and will continue until everyone involved in PC Beshenivsky’s murder has been brought to justice. “
Piran Dhitta Khan, who is still at large, is now 68-years-old and is thought to still be living in Pakistan after fleeing the country following the shooting.
Det Insp Atkinson said that police are continuing to trace Khan and appealed to the public for information that could lead to his capture.
He added: “He is thought to be living in Pakistan and we are again appealing directly to the people of Pakistan, as well as those in West Yorkshire and across the country to come forward and provide information on his whereabouts.”
Mother-of-three PC Beshenivsky, who was also a stepmother-of-two died after she was shot in the chest on the same day as her daughter Lydia’s fourth birthday.
The deputy Lord Mayor of Bradford, Coun Alun Griffiths, was among those who attended her memorial service in Norfolk Gardens today.
He was joined by Deputy Chief Constable John Robins, and Chief Superintendent Scott Bisset, on behalf of West Yorkshire Police and the Bradford district.
A minute’s silence was observed during the ceremony at 3.30pm - the time of the call to the travel agents in Morley Street, where PC Beshenivsky was shot and fatally wounded attending the robbery.
Coun Griffiths, said: “The people of the Bradford district appreciate and respect our serving police officers and the risks they face daily in carrying out their duties.
“Sharon made the ultimate sacrifice that day to protect the people of Bradford. And that dedication to duty is the same dedication we see from Officers and Police Community Support Officers every day throughout our district.”
A £20,000 reward is on offer for information leading to Khan’s capture. Contact the independent Crimestoppers charity anonymously on 0800 555111.