911 calls. What are they really saying in their statements.
Motive, means, and opportunity
MOTIVE, MEANS, AND OPPORTUNITY
When developing your theory or theories about what happened, it's important in violent crime investigation to give equal consideration to motive, means, and opportunity. A lot of the literature on serial killers and repeat offenders is too heavily slanted toward motive and motive-based typologies. Equally, if not more important, is means (who had the physical strength to commit this particular crime) and opportunity (who had access to or could have been present at the crime scene). It's helpful to create what is known as a time line, which accounts for the whereabouts of all the principals in the case before, during, and after the crime. Suspects can be systematically eliminated one-by-one on the basis of opportunity alone. You can always go back and consider motive and means later. Criminal personality profiling should be reserved for when there is no apparent motive.
Above statements are credited to Dr. Tom O'Connor.