THOUSAND OAKS, Calif. (KGO) -- A sequential model two American professors came up with to help us understand mass shootings at schools may provide insight into the deadly attack on a popular bar in Thousand Oaks.
Ian David Long, 28, has been identified as the suspected gunman in the mass shooting at Borderline Bar & Grill.
RELATED: Thousand Oaks shooting survivor also survived Las Vegas shooting
The shooting happened late Wednesday inside Borderline Bar & Grill. At least a dozen people were killed, including a sheriff's sergeant, Ron Helus. None of the other victims have been identified.
Police are still searching for a motive. What lead Long to commit mass murder?
RELATED: What we know about Thousand Oaks shooting suspect, Ian David Long
General strain theory dates back to the 1930's and was further developed in the 1990s by Robert Agnew - to understand what types of societal "strains" or "stressors" which lead to criminal behavior.
In 2009, two American professors, Eric Madfis and Jack Levin, came up with a sequential model to understand mass shootings at schools.
Although the Borderline Bar & Grill shooting was not on a school campus, it was a place frequented by college students. The Madfis & Levin model may provide insight.
The Madfis & Levin model suggests a shooter goes through five stages before committing a mass murder.
1. Chronic strain
2. Uncontrolled strain
3. Acute strain
4. The planning phase
5. The attack
Chronic strain refers to repeated trauma - bullying, isolation etc. In David Long's case what led up to his PTSD may fall in this category.
TAKE ACTION: Help for veterans of all eras, and their families
Uncontrolled strain is when an individual starts to exhibit delinquent behavior - in Long's case we've heard of reports of police being called to his home multiple times.
Acute strain is "the straw that breaks the camel's back." It's usually a specific event involving real or perceived rejection in some way. The event triggers the would-be shooter to start the planning phase.
RELATED: Napa woman who's niece of actress Tamera Mowry identified as Thousand Oaks mass shooting victim
The planning phase can vary in length from a few hours to years.
Then, the attack phase: where the person actually carries out an attack, usually in a place where they will have a high casualty count like a school or bar. This is where firearms expertise can play a factor; the person must actually be able to use the weapons they choose.
RELATED: Father identifies son as one of 12 slain in massacre in heartbreaking press conference
So, as we start to get more background information on David Long from the Thousand Oaks shootings - you may start to see some facts fit into this model.
To be clear, experts agree that there's no real profile for a mass shooter, but models like those developed by Levin & Madfis help to understand the journey these troubled individuals go through before committing an atrocity.
See more stories, photos, and videos on Thousand Oaks mass shooting.
Thousand Oaks shooting: What led Ian David Long to commit mass murder?
THOUSAND OAKS MASS SHOOTING