ok now with the help of FaldeusSama i can understand better of what happened the last chapter and i can imagine that indeed it doesnt make sense that kusorea investigates the case and then claims she murdered her sister, so my best guess in this chapter is that she says that will use him as contractor to clear the mystery of the murder, and she really took the murder attempt strangely well, & my only guess of why mikami really loves milk, i think is a nod of "LEON THE PROFESSIONAL"