On June 3, Memorez Rackley, a mother of three in Utah, called police about her ex-boyfriend, Jeremy Patterson. She said he was stalking her. On one occasion, he had followed her for an hour while she was driving; on another, he showed up while she was at the nail salon.

“He won’t stop,” Rackley told the 911 dispatcher, according to transcripts obtained by the Associated Press.

Three days later, Patterson fatally shot her and her 6-year-old son near a local elementary school before killing himself.

Stalking — which the Department of Justice defines as a pattern of repeated and unwanted attention, harassment, contact, or behavior that would cause a reasonable person to feel fear — is remarkably common in the United States. An estimated 3.4 million people over age 18 were stalked in a 12-month period between 2005 and 2006. The majority of victims are young women between the ages of 18 to 24.

Not all stalking ends in violence, but about 32,000 victims are attacked with a handgun each year. Despite well-documented dangers posed by stalkers, gaps in domestic violence laws mean they can often acquire guns legally.

Federal law bars felons and those convicted of domestic violence misdemeanors from possessing firearms, but that prohibition does not extend to people convicted of misdemeanor stalking.

Earlier this month, Nevada became the latest state to narrow that loophole when it enacted a law that requires those convicted of domestic violence to sell their guns or surrender them to a third party, like a licensed firearms dealer. The law applies to convicted stalkers, too, but not automatically: A court must determine that a victim’s safety is at risk.

Another part of the Nevada bill prohibits those subject to a restraining order and convicted of domestic violence battery from gun possession. The final version of the measure, which passed the state Senate on a 19-2 vote, was watered down to exclude stranger stalking, and did not face opposition from the National Rifle Association, or the Nevada Firearms Coalition.

A victim of domestic violence is five times more likely to be killed if her abuser has access to a gun. Seventy percent of women who were killed by their partners had been abused by that same person before their deaths. And men who kill partners, or ex-partners, sometimes follow a pattern of escalating violence. An abuser might begin with verbal threats, then move on to stalking and physical attacks before killing his victim. Removing guns early in this trajectory is the most effective known intervention to prevent intimate partner homicide.

There is little research specifically on stalking and firearms, according to April Zeoli, a professor of criminal justice at Michigan State University who has studied the link between guns and intimate partner homicide. But stalking is often an extension of domestic violence — about half of all stalking stems from romantic relationships — and statistically, the presence of firearms increases the likelihood of homicide in a domestic abuse situation, she says.

Stalking is a crime in all 50 states, but it isn’t always charged as a felony. The Center for American Progress examined conviction records from 20 states and determined that at least 11,986 people were found guilty of misdemeanor stalking and still permitted under federal law to have guns.

Besides Nevada, at least 16 other states have taken legislative action to try to keep guns from stalkers, according to the National Coalition Against Domestic Violence. California, Tennessee, and Vermont, for example, have laws specifically banning stalkers from buying or possessing guns. In Rhode Island and Delaware, stalking is a felony offense, meaning that those convicted are barred from gun possession.

The Nevada law is “a modest step forward,” says Lindsay Nichols, the federal policy director at the Law Center to Prevent Gun Violence. There has been an uptick in new state-level laws that prohibit stalkers from getting guns: Hawaii, Maine, and Washington, D.C., also closed some of these loopholes. In 2012, Florida passed a law stripping gun rights for those subject to a protective order for stalking. In 2014, Minnesota enacted a law requiring some stalkers subject to a protective order to surrender their guns. In 2015, Oregon barred some under restraining orders for stalking from getting guns. In May, a bill was introduced at the federal level to ban stalkers from possessing guns.

Laws to keep guns away from stalkers are “the very, very, very, very tip of the iceberg,” says Mindy Mechanic, a professor of psychology at Cal State Fullerton who has studied violence against women for more than 20 years. Most people who stalk, she says, have not been prosecuted, because stalking is a particularly challenging crime to prosecute. It’s difficult to define, hard to prove, and is somewhat subjective.

Some stalking victims don’t fully understand that they are victims of a crime — instead perceiving the behavior as a nuisance — and don’t always notify law enforcement. Even when they are ready to take legal action, stalking victims must demonstrate that unwanted advances made them feel afraid or unsafe. Some states add an additional burden of proof by requiring the victim to show that she feared she would be physically (not just emotionally) harmed. And even when a victim pursues legal action, the crime can get pleaded down to loitering or trespassing.

But the key point, says Nichols, is that any stalker can terrorize a victim, who often doesn’t know if or when the stalker will stop — or escalate — his actions. “And that’s clearly someone who shouldn’t have a gun.”