From having no friends to blaming his failures on others to having access to firearms, Isla Vista, California, killer Elliot Rodger appears to fit many criteria of the typical mass murderer -- at least, the profile created by criminology professor Jack Levin. But the template has the same problems associated with any mass killer profile: false positives.

In other words, there may be tens of thousands of people who fit the profile who don’t go on a murder spree like the UC-Santa Barbara stabbings and shootings on Friday night, which left six people dead, including Rodger’s three roommates and two sorority sisters, before Rodger killed himself.

“The value of a mass murder profile is limited,” criminology professor James Alan Fox, Levin’s co-author on “Extreme Killing: Understanding Serial and Mass Murder,” and his colleague at Northeastern University in Boston, told International Business Times.

In fact, the FBI doesn’t even have a mass murderer profile. The bureau’s Behavioral Analysis Unit uses information specific to each investigation to form a profile of the suspect.

In Rodger’s case, his rambling, 141-page memoir provided insight into his motives. The lengthy document details his perceived constant rejections by women and his contempt for women who choose other -- in his eyes, inferior -- men.

“The major motive in almost every mass murder is revenge. In this case, it was made quite explicit by the killer himself,” Levin told IBT. “He has provided much evidence that his motive was to get [revenge], especially with women who have rejected him, but also the popular boys who were attracted to the same women.”

Levin’s profile contains six criteria:

· Chronic depression and frustration

“This doesn’t happen overnight,” Levin said. For example a school shooter might have been bullied from an early age. In Rodger’s case, his memoir indicates that he had been planning his “Day of Retribution” for years.

· Socially isolated

“He just doesn’t have anybody around to give him encouragement and support,” Levin said.

· The person has no friends -- or has friends who are delinquent and may support his violent act

· The person externalizes responsibility

“They want desperately to get even with anyone they feel is responsible for their miseries in life,” Levin said. In his memoir, Rodger appears to blame others for his constant rejection and can’t understand why women don’t gravitate toward him.

· The person suffers a catastrophic loss: for example, a girlfriend’s rejection

· The person has access and training in the use of firearms

Levin said the criteria are cumulative, meaning someone who is frustrated and depressed but doesn’t externalize responsibility might commit suicide instead of mass murder. Someone who is socially isolated and suffers a catastrophic loss but doesn’t have access to guns may not commit a mass killing.

The Isla Vista killings bear some resemblances to other mass murders, Levin noted.

“He’s not the first killer who has targeted a group of people,” Levin said.

For instance, George Sodini’s hatred for women who ignored him spurred him to open fire in 2009 at an L.A. Fitness in the Pittsburgh suburb of Bridgeville, Pennsylvania.

Then there was the 1989 mass shooting at a Montreal engineering school perpetrated by Marc Lépine, who targeted 14 women after he was kicked out of the school. Lépine believed the women were taking his place in the classroom.

Despite the media attention drawn by mass killings, from the high school killings of the 1990s to the massacres at the Aurora, Colorado, movie theater and Sandy Hook Elementary School in Newtown, Connecticut, (both in 2012), such murders comprise a tiny sliver of all homicides. FBI estimates say fewer than 5 percent of all murders involve four or more victims.

But that rarity also means that, for the most part, mass killings are unpredictable, Fox said.

“The good news is that it’s rare. The bad news is that anything that’s rare is impossible to predict,” he said. “Rare is a statistical fact of life.”