Heads turned and jaws dropped late Monday after a tweet by a prominent white nationalist was retweeted by the Alameda County Sheriff’s Office and on display for about 45 minutes before being taken down.

By then, screenshots of the retweet, which featured a Periscope live-streamed broadcast by prominent white nationalist Richard Spencer, had drawn responses from journalists, community activists and observers and begun to spread across social media.

Reached for comment, a sheriff’s department spokesman repeated the department account’s tweeted statement of error, attributing it to a wrong button that was touched while trying to close viewed material sent to the department’s account.

“I’m reading up on recent events, and preparing for the upcoming rally in Berkeley, trying to get ready for the possibility of conflict,” Alameda County Sheriff’s Sgt. Ray Kelly said. “I clicked a link that took me to a presser, then tried to close it by hitting buttons.”

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Kelly said the department regularly sifts through reports from other law-enforcement agencies, media outlets and open-source intelligence.

“That’s how we get information. Obviously, we’re in planning stages. Part of that is doing homework using social media, seeing what’s going on, what kind of rhetoric, what level of sophistication,” he said. “If we didn’t do our homework, we wouldn’t be doing our job.”

The Berkeley rally, set for Aug. 27 at Martin Luther King Jr. Civic Center Park, aims to counter Marxism in America with a lineup of alt-right speakers, and is one of several planned in the Bay Area and beyond.

That was an accidental retweet and was in no way done intentionally. — Alameda County Sheriff (@ACSOSheriffs) August 15, 2017

We are working to take this accidental retweet down. It is not showing up in our feed for is is to delete. — Alameda County Sheriff (@ACSOSheriffs) August 15, 2017

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Contact George Kelly at 408-859-5180.