What broke my heart was how sad his father was when I told him, he said he trusted the son the most.
At eighteen, the boy is an adult and would take full responsibility for his actions and inactions. Parents indeed need to closely monitor their children's activities online, but at that age, it will be very difficult to watch over that boy. This child simply chose to be a criminal, maybe he was influenced by friends or other agents of socialisation.
Instead of closely monitoring, supervising and making them feel deprived of their freedom, I think educating and talking to them regularly can be more effective.
If a child grows up and makes mistakes, it is mainly the parents' fault, not theirs. As parents, we can't just say we are proud and believe in our children, but we never take the time to teach or care for them.
For me, if a child is still under my roof, I would closely monitor their income and expenditure. If he is spending more than I think he should, it will be the right time to investigate his sources of income. It is also important to always investigate the source of your children's income. Don't rely on what he or she told you.
But do it quietly and silently because everyone needs privacy. Although we as parents need to be responsible for our children, they also need to receive special respect from their parents.