Crum, who is survived by a wife and two children, was a former Delbarton police chief and county magistrate who resigned his post to run as a civilian for sheriff last year.
Residents had praised his new drug crackdown, dubbed Operation Zero Tolerance. It had already led to dozens of indictments, so his friends and supporters couldn't help but suspect a connection to his death.
Dallas Toler was appointed to take Crum's magistrate position a year ago when Crum stepped down to campaign for sheriff.
Their goal was mutual: to put a big dent in drug trafficking in the county.
"At least four or five of us have gotten threats," Toler said. "Any time you come in and make an impact on dope and drugs, it's just part of the course. Eugene made a big lick on drugs down here. We all have."
Toler, still in shock, couldn't say whether he feels safe.
"Anything can happen," he said. "This could have been any one of us."
Federal and state law enforcement also have fought the state's prescription drug trade, with federal officials saying in February they had prosecuted 200 pill dealers in the past two years.
On a sign in the parking lot where Crum died, Chris and Christina Endicott scrawled a note expressing love for Crum's family.
"You are family. The best sheriff Mingo has ever seen," they wrote. "Our hearts are broken, along with Mingo County. We love you so much."
The death resonated across the small state. At the state Capitol in Charleston, lawmakers, legislative staff and others wore black ribbons on their lapels, and Capitol police put black stripes over their badges.
A visitation and funeral service are planned for Crum this weekend in Delbarton, according to the West Virginia Sheriff's Association.
Although there is no indication of any connection, Crum's killing comes on the heels of a Texas district attorney and his wife being shot to death in their home over the weekend, and just weeks after Colorado's corrections director also was gunned down at his home.
Those bold killings and others have led authorities to propose more protection for law enforcers.
Williamson, a town of 3,200, sits along the Tug Fork River in a part of the state long associated with violence. Mingo and neighboring McDowell County are home to the legendary blood feud between the Hatfield family of West Virginia and the McCoy family of Kentucky.
Crum's county was dubbed "Bloody Mingo" during the early 20th century mine wars, when unionizing miners battled Baldwin-Felts security agents hired by the coal operators.
Crum's killing saddened and disturbed Maricopa County, Ariz., Sheriff Joe Arpaio, who has described himself as "America's toughest sheriff" and is a national hero to conservatives on immigration issues.
It's unclear whether Crum had been threatened, but Arpaio has been.
"Inside one year, two of my deputies were shot, one killed and one nearly killed, and now elected law enforcement officials across the nation seem to be being targeted," he said. "The brazenness of these acts is confounding."