On the whole, the San Francisco Police aren't an ironic bunch. Even when they're obfuscating, they manage to do it in a straightforward way.

But, as the sixth anniversary of Hugues de la Plaza's gory demise comes and goes this month, there is real irony to supplement the sorrow and anger over the unresolved death of a man who would have been just 42 this week. The dual French citizen, readers may recall, was in June of 2007 discovered dead with three gaping stab wounds in his blood-spattered Hayes Valley apartment. The blade was never recovered; police theorize that de la Plaza either fastidiously cleaned it in his dying moments and returned it to a drawer or otherwise disposed of it so proficiently that it remains lost to this day. Buttressed by the medical examiner's finding that de la Plaza's manner of death was "undetermined," the police advanced the hypothesis that he died by his own hand. "As goofy as that case is, we're certain the suicide theory will pan out," a high-ranking cop told SF Weekly back in 2009.

That has not happened.

And here's where the irony comes in: The police have exerted a great deal of effort in justifying why they've exerted so little effort in resolving de la Plaza's death. And, in doing so, they've engineered a situation in which the case, unlike the man, has been granted eternal life.

Semantics may not be a subject taught in police academy classes. Regardless, the SFPD has demonstrated outsized ability in this field.

The word choice used in categorizing the de la Plaza matter hasn't helped advance a case unambiguously viewed as a murder everywhere on planet Earth outside the Hall of Justice at 850 Bryant St. — and certainly hasn't consoled François and Mireille de la Plaza over the death of their only child. Alas, there are limits to what you can accomplish with mere wording.

But you can do a lot: The medical examiner's "undetermined" ruling allowed the police to push forward with their "goofy" suicide theory — but, per a police statement, the department also "handles and investigates all 'undetermined' deaths as if they were homicides."

Since the de la Plaza case remains an "open investigation," the police needn't divulge details about what, exactly, is being investigated. And since it's a "homicide" — or, rather, categorized as tantamount to one — the SFPD is further protected from being compelled to reveal details at any point in the future, regardless of case status.

De la Plaza's death did not register as another murder — let alone an unsolved murder — in a year when homicides edged toward the dreaded 100 mark. Yet the SFPD has indemnified itself from having to explain what it's doing to solve a case its critics claim the department has little desire to solve.

That's a pretty neat trick.

It's an open question how long an "open investigation" can last. Police spokesman Officer Albie Esparza notes that the Zodiac killings are also categorized as an open investigation. So don't bother making any requests regarding that case, either.

French investigators, however, didn't make requests. They made demands. And, in 2009, a federal judge — an . one — sided with them. The court ruled that all forensic evidence in the de la Plaza case must be packed up and forwarded to Paris. And, unlike the SFPD, French investigators went ahead and ran DNA tests (presumably, their techs didn't snort the evidence).

In August 2012, François de la Plaza told us that another person's DNA was discovered on the crushed wristwatch Hugues wore on the night of his death — strongly indicating a physical confrontation. Three years prior, French authorities determined the case to be "100 percent homicide" — the identical ruling reached in an SFPD-commissioned freelance analysis by former San Francisco medical examiner Dr. Michael Ferenc. The police received Ferenc's report in February of 2009, but neither the de la Plazas nor their lawyer knew about it until, somehow, a copy was obtained by CBS' 48 Hours Mystery some eight months later.

The SFPD, in 2009, told your humble narrator that the manner of de la Plaza's death was "undetermined" and his was "a suspicious death." They told us the same in August of last year, and repeated that line this month, too.

The French aren't planning to send a drone our way to fire missiles at suspected killers. Yet the spectacle of foreign officials coming in and yanking evidence away from the local police force is something you'd expect to befall a guns-but-no-shoes outfit in some backward and corrupt failed state — not a department currently funded to the tune of $528 million in a city touting a budget creeping toward $8 billion.

But it goes deeper than that. The shame here is collective; this was San Francisco trying, and failing, to be a fully formed and grown-up city.

As for when the disgrace will be ameliorated, that remains "undetermined."