FULLERTON – The hacker group Anonymous threatened to disrupt the Fullerton Police Department’s website and email after the death of Kelly Thomas, a mentally ill homeless man last month following a confrontation with police officers.

The group is demanding the resignation of Police Chief Michael Sellers, the prosecution of the officers involved and the city to pay out $5 million to the family of Thomas, 37, who died July 10. Police said Thomas resisted while officers were investigating reports of an attempted car burglary. Six officers responded to subdue him, and a bloody photo showing Thomas’ injuries has received national attention.

As of Sunday evening, the police department’s website was working normally. Anonymous put Sunday at noon as the time of an online attack.

In an online letter dated Aug. 5, a writer signed as Anonymous accuses the police department of attempting to cover up the incident. The loosely organized group’s unidentified members organize online protests and attacks on institutions believed to be involved in censorship

“This is not just a brutal attack against another human being, but an attack against human rights,” the letter said.

On Wednesday, Sellers was placed on medical leave. The six officers involved have also been taken off street-duty. Sgt. Andrew Goodrich of Fullerton police said the department was aware of the threat from Anonymous, and is taking physical and virtual precautions.

“Our citizens may be denied Internet communications with the city and police,” he said. “However, city services including police and fire, will continue to operate as usual.”

Goodrich stressed that if fault is found with officers, they will be held accountable.

“We are asking people to be patient and let the investigation be completed,” he said.

Ron Thomas, Kelly Thomas’ father, said he had heard about the threat and didn’t condone it. Instead, he said he appreciated peaceful support from the community and beyond. Supporters plan to continue protests at the Fullerton police station on Saturdays.

“We’re not going to do anything that’s violent or illegal,” he said, adding supporters could also visit the Kelly Thomas Memorial Fund website, ktmf.org.

In San Francisco, Bay Area Rapid Transit district officials were working Sunday on shutting down a website listing the names of thousands of area residents who are email subscribers to a legitimate BART site. Hackers who also say they’re part of Anonymous targeted BART after officials shut down underground cellphone service Thursday to thwart a planned protest on the recent fatal shooting of a homeless man by police.

The Associated Press contributed to this report.

Contact the writer: ckoerner@ocregister.com or 949-454-7309