This case had a particularly depressing end to it, didn't it? In a lot of the cases, some little bit of info comes to light during the winding up of things, which often gives the murderer a glimmer of hope and possible future redemption and healing. And/or Kindaichi offers some words of encouragement to the culprit. Here, it's just... the girl with a terrible life who was going to kill herself was rescued by a perfect guy, who was murdered by three idiots, and she lost the baby as a result... case over, she goes to prison (presumably). She's probably going to hang herself in prison now that her revenge is complete and she has nothing left to live for (although I guess she could still want to take out the third idiot). Page 20 is right that it has "an unsatisfactory feeling." It's quite sad.