In presenting a defense regarding a criminal complaint, the simplest approach is usually to prove that the alleged offenses didn't happen or that the defendant isn't the person who did them. Some cases, however, call for a different tack because there's no basis for the defendant to claim complete innocence. Even in situations where you might have done something bad, there's usually more to the story than that. In the parlance of a criminal law attorney, these other factors that explain what happened are called extenuating circumstances.
Notably, this approach is less about getting a defendant off the hook than it is about trying to have charges reduced. There is a degree of admission of guilt in most of these cases, or there's at least an admission that the defendant didn't fully understand what the law actually was at the time they committed the alleged offense.
One of the more commonly cited forms of extenuating circumstances is when there's a specific outside influence on the defendant. A significantly younger minor in a relationship with an adult may not be seen as having the same level of culpability for crimes committed as a consequence of that relationship. If the minor were acting as a drug courier on behalf of the adult, for example, there's an argument for leniency because of that set of extenuating circumstances. A similar argument could be made if a younger sibling were pressured into participating in gang activity by a sibling or a close relative.
State of Mind
The mental condition of a defendant at the time of an offense also is sometimes factored into how a prosecutor brings charges or a judge handles sentencing. At a societal level, it would feel wrong to aggressively sentence a former soldier with PTSD for their involvement in a fight, for example, as long as they had no history of criminal conduct. There's a strong possibility that the court may offer leniency with some contingencies attaches. Someone who cited mental duress may be asked to complete some form of counseling with a suspended sentence awaiting them if they prove uncooperative.
Expected Time in Jail
If an 85-year-old was facing 10 years in jail and showed signs of ill health, there's a real possibility the sentence would effectively be a life sentence. That fact can be seen as an extenuating circumstance, especially in dealing with non-violent offenses.