Of course not. But the law itself begins with an assumption of innocence and prevents you from going out and administering that justice, yourself. The system is designed to deliver not only a truthful verdict, but a fair sentence. In the case of your hypothetically murdered family members, unfortunately, we have a system that has gotten to the point where a guilty person may or may not pay the price for the crime committed against you. If an innocent person is executed for these murders, how does that give you justice? How magnified would your sorrow be if, down the road, you discovered that you helped put an innocent man to death as a means of getting justice for your departed?
I said that guilt must be proven beyond doubt, in both of my posts. The argument about the innocent being executed doesn't hold water after that.