"We live in a culture of celebrity worship," says psychologist John D. Moore, who has studied obsessive fandom. "And for people with mental-health issues, it can become more than celebrity worship. It can become a central focus for them." Sometimes, he says, it becomes a violent one.
The author of "Confusing Love with Obsession," Moore advises celebrities and their security staff on dealing with potentially dangerous fan situations.
He says the obsessions generally fall into two categories: Love obsessions, he says, can occur when a super fan, who may suffer from such mental-health issues as schizophrenia and bipolar disorder, develops an intense romantic attachment.
"They are stalking them because they feel they have a personal connection with the star, and that the star has a connection with them," he says.
Other stalkers who have erotomania, a romantic fixation, become convinced that a public figure is using the media - news reports, for example, or songs - to communicate directly with the fan.
"And here again, the person feels they have this strong, strong connection to the star," Moore says.
The situation can become dangerous when the obsessed fan feels slighted, according to Moore. Emails go unanswered. Facebook messages are ignored. Instagram comments are deleted.
"When the person feels minimized, when they feel jilted, discounted, anything like that," he says.
"They can kind of flip to this other side, where they escalate their attention-seeking behaviors. And then it can turn into something violent."
With almost every deranged celebrity fan, Moore says, there is a trail of attempts to make contact.
"There's usually always a pattern. It's not just something that happens once," he says.
One letter from a fan professing undying love for a celebrity may not raise any red flags, he adds, but if a second, third or fourth arrives from the same person, it needs to be taken seriously.
The threat to celebrities is pervasive enough to push many of them to take extreme measures. Rapper 50 Cent has said that he spends $20,000 a week - that's more than $1 million a year - on security. Others, such as Beyoncé, almost never interact directly with fans.
"Because just like the paparazzi can follow someone around, the stalkers do, too," Moore says, adding that stalkers are often intimately aware of the comings and goings of those about whom they obsess.
"It's very terrifying to think that you really don't have a lot of privacy, and that you have to watch everything you do."
Despite heightened security, celebrities can be vulnerable even when they perform. Grimmie's mentor, Adam Levine, was accosted by a fan during a concert in April, 2015. The same month, rapper Plies was thrown off a Tallahassee stage by a fan who felt disrespected.
In the worst instances, Moore says, some celebrities feel there's nowhere they can be safe.
"Celebrities become so terrified that you just don't see them," he says.
"They close themselves in."
