Humboldt County homicides are continuing at a rate unprecedented in recent history.

Arcata police responded to the 2000 block of Eastern Avenue at about 11:15 p.m. Saturday, May 9, to find 38-year-old Trevor Mark Harrison bleeding from a gunshot wound to the shoulder. As detectives processed the crime scene — where police say a pre-arranged marijuana deal devolved into a robbery attempt that went awry — Harrison was pronounced dead at a local hospital, making him the county's sixth homicide victim so far this year.

If the current pace holds, Humboldt County is set to match last year's total of 16, the most the county has recorded in at least 30 years (data prior to 1985 is not immediately available through the coroner's office). Perhaps equally alarming is the fact that the 33 homicides the county has totaled in 2013, 2014 and thus far in 2015 equal the highest three-consecutive-year tally in the modern era, which was set in 1991 through 1993. And, as of this writing, we are only 132 days into the year.

Over the last 30 years, Humboldt's homicide rate has fluctuated, spiking and falling between the low of four homicides in 1989 and last year's high of 16, with an average of 8.5 killings a year. Experts say this type of statistical variation is to be expected in a county with a relatively small population. But how do we know when an outlier has become the norm, much less pinpoint a cause?

Humboldt County District Attorney Maggie Fleming said she's very reluctant to attribute the recent spike to a specific cause or to say it's going to continue. "I do believe there can be substantial variation in annual and short-term frequency of events, such as homicides, even in the absence of changes and underlying causes," she said, but quickly added there are some trends and themes. "As we know in our community, violence is often linked to substance abuse and mental health issues, so we really need to do all we can to address those specific issues in our community."

With five of Humboldt's homicides this year under investigation by his office, Humboldt County Sheriff's Lt. Wayne Hanson thinks society as a whole has simply become more violent. If pressed to point to an underlying theme in Humboldt's recent killings, Hanson said a lot of them have a "nexus to marijuana."

That holds true with Harrison — police say the suspects had apparently arranged to purchase marijuana from or sell marijuana to him before attempting a robbery that ended with the shooting — but it's unclear how prevalent the theme really is. Of the 22 killings stemming back to the start of last year, only four have been publicly linked with marijuana transactions or the industry as a whole. Five of the cases remain unsolved, with no suspects in custody and no publicly known motive. Included in those are the stabbing death of a 14-year-old boy in Eureka, a decomposed body found in a wooded area near Hoopa and a 57-year-old man found shot to death in the Rancho Sequoia area of Southern Humboldt.

Arcata hadn't seen a homicide in eight years when it recorded three in 2013 — a double-murder committed during an alleged sexual assault at a house party and a stabbing during a downtown dispute. Harrison's killing leaves the city looking at four homicides in a 24-month period. It's hard to make sense of, said Arcata Police Chief Tom Chapman, adding that he'd like to call the spike an anomaly but is hesitant to do so.

"There's no relationship between any of these cases, other than to say: You bring a gun to an event and bad things are going to freaking happen. ... You bring out a knife, and something bad is going to happen," he said.

"It's frustrating," the chief continued, his voice trailing off slightly. "There seems to be this devaluation of human life."