The FBI must do better handling tips and leads about people who may carry out violent acts – including assessing whether individuals with mental health problems pose legitimate threats to natural security, according to a new report by a justice department watchdog.

The report from the inspector general’s office identifies what it says are weakness and inconsistencies in how the FBI evaluates tips on homegrown violent extremists – people who are motivated by jihadist ideology and are operating in the US independent of foreign terrorist organizations.

The report underscores the FBI’s challenges in preventing violence from people whose actions and ideology may be disturbing without violating federal law. Those difficulties attracted fresh scrutiny in recent years after several people the FBI once investigated but did not arrest because they had not broken the law later went on to commit attacks, including the gunman in the 2016 Pulse nightclub shooting in Orlando.

The FBI in 2017 directed its field offices to study whether they had properly handled terrorism-related tips over the prior three years. That internal review found problems in the way the FBI had handled 6% of those threat assessments, but even after that review, not all field offices adequately followed up on the fumbled tips and leads, according to the inspector general’s report.

In addition, the report says, the FBI has said there is an increase in the number of reports it receives on people with mental health problems, but the bureau lacks a consistent strategy for dealing with that information. In some cases, the FBI refers the individuals for mental health evaluations and in others refers them to family members for monitoring, according to the report.

The challenge is compounded because many individuals who are reported to the FBI for suspicious behavior or radical ideology are dealing with mental illness and are not actually a threat to national security.

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The report’s seven recommendations, which the FBI says it agrees with, are largely bureaucratic in nature, relating to how field offices processes and categorize information they receive on potential threats. But the issue is significant for the FBI and justice department given that so-called homegrown violent extremists are blamed for more than 20 attacks since September 11, 2001.

In several of those attacks, the FBI spent months looking at the eventual perpetrator but closed out its inquiry after either not finding a crime or a basis for continued investigation.

“This is a particularly challenging area for the FBI because of the need to preserve constitutional protections while maintaining national security,” said the inspector general, Michael Horowitz, in a video statement accompanying the report.