If Samuel and the Bowers family came to reprimand him, he would not be able to answer them.
The death of a person was just like the dousing of a candle. Even though Thomas could not figure out Melissa's real intention, he figured it would still be meaningless for the cop to get to the bottom of the matter. It would not change the fact that the Nichols family had been wronged.
He had lost Melissa forever.
He had to accept the cruel reality no matter what.