Means, Motive and Opportunity

That criteria is perhaps the most well known in determing suspects of crimes, but the second criterium troubles me.

Below are simplified definitions of each criterium.

The means are myriad, they can be resources, weapons, persons, anything which assisted in the commission of crimes.

Motives are the assumed reasons for crimes. Crimes may be a response to offenses, thus the commission of a crime might be the motivation itself, that of inflicting damage or death, or it may be the means by which one achieves the motivating goal, perhaps money, possession of another person, et al.

Opportunities exist when there is sufficient time and ability to have committed crimes.

What makes determining motive so difficult for me is not in understanding what can be motives, but in being certain of the intended motives for crimes. To some, they are obvious, but about when alternative motives have close to as much legitimacy as assumed motives? Or when defendents' claimed reasons for crimes cannot be disproven? Well, the initial answer should be, I believe, to discredit the alternative motives, if one is certain of the truth of the assumed motives, but one should go where evidence leads and be careful to not mold evidence to suit theories. Unfortunately, this isn't a popular notion, that a benefit from an action is not necessarily the reason for the action, or some criminal activities.

Above is why I am a terrible conspiracy theorist, or a terrible thinker, because if my logic is not too insane, what I am alluding to is an important, to me, ethical question: Is it right to convict in one's mind another person because he might, even if indirectly, obtain something which belongs to another, and not answer the question of whether his stated reasons for his action are sincere? Does hypocrisy prove him dishonest? Is it even pragmatic to expect non hypocrisy in whatever the situation happens to be? To me, conviction without even an ounce of concern of these questions is cynical and amoral, and I hope not to be that way, even if I come across as stupid.