The Philadelphia Police Department said the bogus tip was received on 18 July through a public website where members of the public can share information on unsolved homicides. The AI agent wrote that it "may have information" on a case and claimed to have seen "someone matching the description", police said in a statement.
The tip was flagged as spam and never passed on for investigation. Police said there were no signs that any departmental systems were compromised.
According to the police department, citing information from Anthropic, the AI agent had been running a test that involved interacting with randomly selected websites when it generated the false report.
Anthropic discovered the breach on 28 September, more than two months after the tip was sent, and shut down the automatic testing process behind it. However, police said the company did not notify authorities for another nine days, until 7 October.
"The company must strengthen its safeguards to prevent similar incidents from impacting city systems without the city's knowledge," Philadelphia police said. "The two-month delay in detecting and reporting the incident to the city is unacceptable."
The incident is the latest in a series of episodes involving autonomous AI agents behaving unexpectedly, including hacking systems and taking control of platforms.