Last week’s killings in Colorado have led to important conversations about how to prevent these atrocities in the future. Gun control is one. Another is how to spot and help potential killers before they strike.

WebMD had an insightful interview with expert Jack Levin, PhD, a professor of sociology and criminology at Northeastern University, who has written many books on violence. The main problem with profiling mass murderers, he said, is this: “[The profile] applies not only to mass killers but to millions of other people who have never hurt anyone. So you have to be careful where you apply it.”

Keeping that in mind, here’s Levin’s list of characteristics these violent killers have in common:

–Chronic depression
–Social isolation
–Blaming others (as opposed to themselves) for their problems
–A catastrophic loss (job, relationship, money, etc.)

In addition, Levin notes one childhood red flag to which parents should pay close attention: extreme violence toward animals, particularly a family pet like a cat or dog, with hands-on, sadistic acts as stabbing, mutilation, or suffocating.

Read more here about how to identify the profile of a killer—and what to do if you suspect someone needs help.