Even before he arrives in Northern Virginia, the new fire chief for one of the country’s wealthiest suburbs heard the reason some people do not want him there: his skin colour.

The hoods and robes of today’s bigots are anonymity and wi-fi.

And in Fairfax County, the digital demagogues are in full terror mode, throwing all the hate they’ve got in a scathing, online attack on the incoming fire chief, John Butler.

“It’s a great time to be Black in America. If you can spell your name, you can get a free ride through college, be fire chief or even President. Doesn’t matter if you’ve never achieved anything more than having dark skin!”

That’s one of the mildest comments on the notorious, local online forum known as Fairfax Underground.

Never mind that Butler has been leading the fire department in Maryland’s Howard County for almost three years. Never mind that he has been a firefighter and paramedic for 25 years, did two tours of duty with the Marine Corps, was educated at Harvard, Johns Hopkins and the University of Baltimore.

Nope. They’re freaking out because he is black.

“Next white boys won’t be hired,” another poster warned.

The county has launched an investigation into the hatred, trying to determine whether those posts are coming from inside the Fairfax County Fire and Rescue Department or the county government.

“Racist, sexist, harassing or retaliatory comments like those on Fairfax Underground are reprehensible,” County Executive Bryan Hill said in a statement.

“Any employee found to have participated in posting these comments will be subject to severe disciplinary action. It saddens me that in 2018 our country continues to deal with the hateful actions of a select few.”

That is one of the problems here. Is it one person? Twenty people? A troll from Texas? Russian bots? Are any of them firefighters?

This was the big question the county faced two years ago when cyberbullying led to a sweeping investigation, a resignation and a suicide in a Virginia forest.

Much of it unfolded on Fairfax Underground.

“Fairfax Underground is not a county site,” said Sharon Bulova, chairwoman of the Fairfax County Board of Supervisors. “We even block it from the county’s wi-fi.”

The site is a primitive, digital bulletin board where folks gossip — nearly all of them anonymous — about everything from school test scores to memories of old-time shops to the neighbourhood drug dealer to sexcapades among divorcees.

“It’s ugly, it’s nasty, it’s disgusting,” said Bulova. “But it’s not illegal to say ugly things.”

County investigators do not have a court order to probe the online comments as a criminal matter, but they are able to examine them as a personnel issue.

So why write about it? Why give these trolls a megaphone?

It is something that fire service consultant Dave Statter struggled with before he wrote about the Butler hate on his blog, Statter911.

He came up with a solid reason, quoting former United States Supreme Court justice Louis Brandeis, who said that “sunlight is said to be the best of disinfectants”.

So let’s shine a light on this.

Many of the posts have insider details.

I asked someone on the inside to look at this most recent hate splatter.

“Those posts are from ffx FD,” my source texted. “There is no way the outside world would know some of that.”

The forum has a frightening level of granular detail. Where a lawyer’s children go to school, the colour of a female firefighter’s underpants and what an officer scored on his test are all here. Nothing is vague except the identity of the person doing the writing.

“Some days, it took everything I had not to eat my gun,” one Fairfax first-responder who was cyberbullied on the site told me.

Two years ago, the intensity of the attacks might have played a role in 31-year-old Nicole Mittendorff’s suicide. The firefighter’s death put a spotlight on the horrific posts about her on the website, attacks that continued even after her body was found.

Investigators said they drew no direct line between the harassment and her death. Family members said Mittendorff talked about the attacks and was stung by them, but chose to ignore them and move on.

No one will know how the attacks haunted her. She took those answers to the grave. But her death did let us know that all was not well in the fire department.

So the department hired a woman to help to change the hate culture. That woman, longtime firefighter, battalion chief and national counterintelligence expert Kathleen Stanley, resigned and recently filed a lawsuit after her suggestions were ignored and the hatred continued.

The department has faced a long history of lawsuits alleging discrimination. The most sweeping one was filed in the 1970s and resolved in 1982, creating a permanent consent decree banning the county from discrimination.

This time, the county hired an outside consultant to tell them whether they have a problem. They have a problem.

Chief Richard Bowers Jr, who spent about half of his five years as chief fighting this battle, resigned. After a search, Butler was chosen to succeed him last month.

And 24 hours later, the hate parade began.

The comments were filled with the n-word, complaints about minorities “taking over” and the prediction that all of Fairfax will burn.

That one’s funny. Only about 18,000 of 95,000 emergency calls to the Fairfax County Fire and Rescue Department each year are about fires. And even that number has been steadily declining.

Bulova added that although Butler has an exemplary career in the field, they didn’t hire him to get out there and squirt a hose.

“There are many who can put out a fire,” Bulova said. “We have a whole fire and rescue department who are very skilled. Chief Butler is going to be an exemplary manager.”

There are other fires he has to put out.

Butler “respectfully declined” to comment when I reached him. He is still in Howard County and does not start his new job until September 1.

The truth is, he’s not stepping into anything new or specific to Virginia.

“Sometimes, I feel like the country is in a bad mood, and people feel more liberated to say things and post things that they never dreamt of five or six years ago,” Bulova said.

The closet bigot is especially problematic in this field — first-responders. The stakes are higher than in many workplaces.

In this world, when someone is facing a wall of fire and the building is coming down, every vulnerable firefighter has to wonder whether a colleague at the other end of the hose is the poster known as “monkey fire department” or “Whoops! Burnt another one!”

Both openly pine for an all-white world.

A first-responder who faces danger every day told me: “The problem is, you never know who the enemy is.”

The enemy is hiding in plain sight, and digital pseudonyms are their new hoods.

That’s why we have to care.

•Petula Dvorak is a columnist for The Washington Post’s local team who writes about homeless shelters, gun control, high heels, high school choirs, the politics of parenting, jails, abortion clinics, mayors, modern families, strip clubs and gas prices, among other things. Before coming to the Post, she covered social issues, crime and courts