He retweeted a video showing a white nationalist press conference.
"For me this was a very bad mistake, and for that I'm sorry," Alameda County Sheriff's Department Sergeant Ray Kelly said.
Sergeant Ray Kelly with the Alameda County Sheriff's Office is apologizing for a retweet on the department's official Twitter account.
It shows the page of white nationalist Richard Spencer and video of a "unite the right" news conference.
Outraged Twitter users were quick to call out the department. Some accused deputies of supporting white supremacists, while others demanded the person responsible be fired.
"It was absolutely an accident. I cannot tell you how embarrassing this has been for me personally. I don't think anyone has been harder on me than myself in regards to this. I do not condone or endorse any type of hate speech," Kelly said.
To make matters worse, Kelly could not figure out how to undo the retweet, and had to get help from the IT department.
We are working to take this accidental retweet down. It is not showing up in our feed for is is to delete.— Alameda Co. Sheriff (@ACSOSheriffs) August 15, 2017
His explanation was that he was researching in preparation for a white nationalist rally planned in Berkeley later this month.
"We in law enforcement rely on social media, really on Twitter to get real time information," Kelly said.
"I think the story he pushed the wrong button is laughable," activist Cat Brooks said.
Brooks does not accept the sergeant's apology. She's convinced this tweet exposed the truth.
"Maybe they didn't mean to share with the world that's the type of material they are watching over at the sheriff's office. The other thought I had today was it might be one of the sheriff's way of passively aggressively responding to the community resistance," Brooks said.
The retweet has been removed, and the department is now focusing on preparations for the "no to Marxism in America" demonstration, and the possibility things could turn violent like they did in Charlottesville.
That rally is scheduled for August 27 in downtown Berkeley's Civic Center Park.