Final answer:
Spree killers like Charles Starkweather are believed to be motivated by personal grudges and unresolved traumas according to retired FBI profiler Gregg McCrary.
Step-by-step explanation:
Retired FBI profiler Gregg McCrary believes that spree killers like Charles Starkweather are motivated by personal grudges and unresolved traumas. This viewpoint is supported by historical cases where individuals acted due to personal vendettas or to avenge perceived injustices, such as the murder committed by Dr. George Darden out of a vigilante desire for justice. The motivation for this type of violent behavior can also relate to wider issues, such as hate crimes or terrorist attacks, where individuals or groups carry out acts of violence based on ideologies or in response to societal tensions.
Answer: d) Personal grudges and unresolved traumas