(CNN) -- Determining how to prevent mass shootings in the United States has been a complicated debate, but there's new evidence that one intervention could play a role in reducing the violence: "red flag" orders.
Extreme risk protection order laws, colloquially known as "red flag" or ERPO laws, allow the temporary removal of guns from people deemed at high risk of harming themselves or others. They've been presented as possible solutions to help prevent the mass shootings that plague the United States.
Preliminary research, published in the journal Annals of Internal Medicine on Monday, suggests that this "urgent" and "individualized" intervention can play a role in efforts to prevent mass shootings.
The researchers requested county court records for the 414 gun violence restraining order cases that were initiated in California between 2016 and 2018. They received 159 records for the research and based their analysis on those cases.
Among those records, the researchers found 21 cases that involved someone who had or soon would have access to firearms and "made a clear declaration of intent to commit a mass shooting" or exhibited behavior suggesting such an intent.
It's impossible to know whether the threatened shootings would have happened, but the orders "allowed for immediate intervention to reduce firearm access, in most instances because of timely reports from threatened parties and members of the public," the researchers wrote.
They added that they "make no claim of a causal relationship" and that "further evaluation of the implementation and effectiveness of ERPO policies in California and other jurisdictions where they have been enacted would be helpful."
Seventeen states and the District of Columbia have passed some type of these laws, and the details vary from state to state.
In the aftermath of two mass shootings -- in El Paso, Texas, and Dayton, Ohio -- that killed at least 31 people this month, attention turned to what could be done to prevent such tragedies. Extreme risk protection orders were among the solutions floated by President Donald Trump.
"We must make sure that those judged to pose a grave risk to public safety do not have access to firearms and that if they do, those firearms can be taken through rapid due process," Trump said at the White House. "That is why I have called for red flag laws, also known as extreme risk protection orders."
The President did not elaborate on what he meant in the speech, so it is not clear whether he was proposing a federal extreme risk protection order law, endorsing an expansion of the laws across more states or simply advocating for better enforcement of the laws currently on the books.
Before the Parkland, Florida, shootings in 2018, five states had such laws: Connecticut (enacted in 1999), Indiana (2005), California (2014), Washington (2016) and Oregon (2017).
After Parkland, laws were passed in Florida, Vermont, Maryland, Rhode Island, New Jersey, Delaware, Massachusetts, Illinois, the District of Columbia, New York, Nevada, Hawaii and Colorado.
Extreme risk protection order laws can vary in detail by state -- such as who is authorized to petition for an order or how an order is implemented -- and such laws remain complex, even for those enforcing them.
How one 'red flag' law works
Sgt. Eric Pisconski, who oversees the Seattle Police Department's crisis response unit, says the unit has done 55 petitions for extreme risk protection orders since 2016. The unit also has vetted 146 people for an initial ERPO and then 33 for potential renewal at the one-year mark.
Of the ERPOs granted, "we have secured a total of 138 firearms from 44 individuals," Pisconski said, adding that 11 people assessed didn't have firearms.
The circumstances around an extreme risk protection order vary. Sometimes, an extreme risk protection order happens when a gun owner tries to kill themselves.
Several people close to that person might call police with concerns that the person is suicidal. Officers might arrive on the scene, have the person undergo a mental health evaluation at a hospital and confiscate the person's gun at the time of the incident. Then, police could file a petition to the court for that person to temporarily lose access to their gun. That way, they won't be able to retrieve it immediately after being released from the hospital.
The same could happen for someone who posts violent threats online.
The person could make comments on social media about killing people, for instance. If someone alerts police to the social media posts, the police could track down the person and determine whether they pose a real threat to the public. That was the case in the Seattle area in 2017, when the Seattle Police Department was notified of a man who was posting threats online to shoot up a church and was facing multiple felony charges based upon his threats and postings.
"We really think that we avoided a potential deadly situation that could have had one or more victims," Pisconski said. The man was arrested with no incident, and police petitioned for a court order to secure his firearms.
Still, that's an extreme case, Pisconski said. "The vast majority of them have been individuals that have had suicidality -- the concern of direct harm to self, not so much others," he said.
"The extreme risk protection orders are designed as a mechanism to temporarily remove a firearm from an individual during a period when they are experiencing a behavioral crisis and there's demonstrated evidence that they are engaging in dangerous or threatening behavior."
Extreme risk protection orders can't stop all gun violence, but Seattle's crisis response unit hopes they could help reduce the possibility of gun violence -- at least among individuals that come to the unit's attention.
"I think that, sometimes, there's a perception that extreme risk protection laws are the panacea, that they're going to stop all mass shootings or be able to catch all potential perpetrators," Pisconski said. "That's not a reality."
There have been some challenges with using extreme risk protection orders as tools to predict and minimize gun violence in communities, including determining when to deem someone a true "threat" to themselves or others and how to petition orders without "criminalizing mental health," Pisconski said.
"It's a sticky situation."
Orders focus on 'dangerous behaviors'
One way to think about extreme risk protection order laws is to see them as "a tool" for the community to de-escalate a situation, according to Shannon Frattaroli, an associate professor of health policy and management at the Johns Hopkins Bloomberg School of Public Health.
The orders are civil and not criminal, Frattaroli pointed out.
Also, "it's important to recognize that mental illness is not a risk factor that we look for when thinking about risks for violence. We know from the data that people with mental illness are more likely to be victims of gun violence," she said, making a point for the public not to assume that mental health problems are linked with dangerous behavior, which can be stigmatizing.
"These extreme risk laws very specifically focus on dangerous behaviors, not on mental health diagnoses, because dangerous behaviors are the important predictors of future violence," she said.
Those behaviors can include talking about harming yourself or others, writing about plans to be violent or threatening someone with violence and having the means to carry out those plans.
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