Steven J. Underwood
Slain master police officer Steven J. UnderwoodHandout: Des Moines Police Department

After Washington police officer Steven Underwood was shot dead in the line of duty, his colleagues made a promise to his widow that they would look after their colleague's son, Esteban, who was only two at the time.

Some 16 years later, 100 of the slain police officer's colleagues from different counties turned out to see Esteban graduate from Woodinville High School in Everett, Washington.

Steven Underwood was shot dead when he stopped four teenagers as they walked along a high way after recognising one of the juveniles was a wanted felon.

He suffered gunshot wounds and died in hospital. The killer was sentenced to 34 years in prison.

The local news source, the Herald, reported that news of Esteban's graduation spread through local law enforcement agencies.

He arrived in his father's friend's patrol car, with a number of other patrol cars and sheriff's office motorbikes joining.

On steps leading to the Xfinity Arena, where his graduation took place, Esteban shook the hands of every one of the officers who had arrived for him.

Esteban's grandmother, Sharron Underwood, told the Herald that it filled her heart with joy to see all of law enforcement officials gathered to celebrate her grandson.