
... it was a trap, it's obviously a trap.
Sargeant betrayed MC because they ramsoned his (or grand)baby (maybe they kidnapped his pregnant wife or daughter and promised their release if he got MC into the trap)
ML wants MC, maybe he desires him, but most probably wants to destroy him, make him grovel at his feet and show him that there's no hope in this crooked world.

.. debts are not hinerited. Is this a korean thing?
The only debt that one has is the one they co-sign, and if they don't, once that person dies, the children can run to a notary and rennounce of the debts. If the debtor disappears, the children have no legal obligation. I know it by experience.
It would be horrible to have your life ruined because of your parents decisions, feels like SK has not improved further than in technology...

Where I live you can inherit your parents debt if they die. Though your parents can get an insurance policy that will guarantee that you don’t inherit their debt once they die and allows you to keep whatever it was that they were trying to pay off.
Now if the parent is still alive, but disappears leaving behind debt then their child will not have to pay it off lest they co-signed
.. He has no proof that our ML killed all those people.
Even if he had, all these could be falsified by a higher power than ML, which is the reason why no real suspects appeared. They are trying to bury it because the killer must be related to a higher power than law.
But you have in front of you a kid that lost it all, even his own memories and identity, and the only person who gave him back safety, a place to belong, a family... you decide to accuse him of being his torturer? What the frick is your end-game here?
This detective is the true example of how good-willed people can be the truly A-holes in a story. He may be trying to do the right thing, but by doing it he's destroying our MC's life.
I'm saying it once and twice, ML didn't do it. The real killer is still trying to end MC, so he's protecting him, while knowing he can't get to the real killer because of his power.