Draper Police Sgt. Derek Johnson with his family.

The Draper police sergeant killed in the line of duty last weekend appears to be the victim of an ambush by a man who reportedly set out with the intent to kill a policeman. We don't know why. We do know the man he took down, Sgt. Derek Johnson, was an exemplary public servant, well liked and well respected. He was the kind of law enforcement officer a community is proud to have on duty.

His death is the latest example of a disturbing trend documented around the country involving ambush attacks on uniformed police. According to the National Law Enforcement Officers Memorial Fund, of the 17 officers killed by firearms by mid-year, seven were killed in ambushes — the largest single manner of death. No officers were killed during that period while trying to make an arrest. Two died while assisting in traffic incidents.

Research shows this is the second year in a row that ambushes have been the leading cause of death among police officers. Experts are at a loss for a simple explanation. Some say it is happening as a result of increasing economic and domestic pressures on people who reach a point of desperation. Others say mental illness plays a role. Some point to the easy availability of firearms.

Authorities began noticing the trend a few years ago. In 2011, Attorney General Eric Holder launched a campaign to review officer safety as a result of ambush incidents, citing the need for research on how to assist officers in protecting themselves against such attacks.

The development mirrors another trend that has also put more officers directly in harm's way. Incidents of so-called "suicide by cop" have become increasingly common in recent years, according to academic research. In 2009, the Journal of Forensic Science reported that between 1998 and 2006, such incidents comprised 36 percent of all cases of officer-involved shootings — about 250 total incidents.

As with cases of ambush killings, psychologists and sociologists will ponder the reasons why. But regardless of the cause, the effect is devastating. Sgt. Johnson leaves behind a wife and young son. He was 32 years old, and already a veteran officer with a sterling service record.

Aside from the impact on his family and the city of Draper, the manner of his death should have a powerful bearing on all local law enforcement. It was senseless, and random, but nevertheless not rare. It is a distressing indicator of a growing menace to on-duty police officers whose jobs are hard enough, and risky enough, to begin with.