I'm going to disagree with this, though it's just my opinion. I think it's possible he WAS always a good father or brother *in the context that they knew him*. I'm likely older than you (if that has any bearing), and I have seen twice in my life a situation where a "perfect" spouse/father/citizen did something drastically, wildly out of character like this (with drastic, life-changing consequences). And another time when said perfect spouse *almost* did. Middle-aged adults can and do 'crack' on occasion, and when they've spent a lifetime cultivating a seemingly perfect life, but are growing more hollow on the inside with each year that passes, it can be as devastating as it is unexpected. Not saying that's necessarily what happened here (I don't have access to all the facts nor do I know his actual frame of mind), but I DO believe his family, friends, and/or colleagues when they say that this "wasn't the Tad they knew."
I've read all the articles and docs, but am open to a slightly different take on this wildly improbable, not-too-well-thought-out flight to nowhere with a 15-yr old student. (Remember, I saw this happen with my own high school teacher and underaged classmate.) Rather than seeing TC as someone who was 'always' a groomer/child predator and who managed to keep that fact hidden for 30+ years, I am open to to the idea that he hasn't always been that way...but that in recent years, dealing with bankruptcy, confronting his own advancing middle-age and physical decline, and pehaps even conflicted about grandparenthood, that he began an internal downward slide. Eg., the story of his singing a song to another student earlier, and her reportedly not really knowing how she interpreted that--seems like there were at least some mixed interpersonal signals happening that could be an earlier clue to psychic shift of mind that was left unacknowledged and not dealt with--eventually blowing up into this horrific episode. JMO (and likely an unpopular one), but I do not see that song episode as "proof" that TC has been a child or adolescent predator and/or groomer all his life, fooling everyone all his life as to who he actually is. Though I may be wrong, all the history and evidence I've read so far seems to suggest (to me) that that song episode was more a red flag or symptom of the beginnings of 'losing his grip' (for want of a better phrase), that never really got acknowleged or addressed, so that his inward downward spiral was allowed to continue. It IS possible to look completely on top of things for 30 yrs in all areas of one's life, and then go completely off the deep end. Though not certain at this point, this possibility manifests itself in the complete irrationality of his actions, to me. It's not mere stupidity that makes a man think he can suddenly walk out on what he's spent 30 years of his life building, to kayak away to Mexico or join a commune for life with a 15-yr old "wife." This is irrational, wholly emotional behavior, that throws all reason to the wind. (I think it's even possible in his confused state, he might actually believe he loves both JC and ET.) Unfortunately, such a crisis is particularly devastating when that involves dragging another damaged, needy individual right down the drain with you.
This is not letting him off the hook (not talking legal insanity, here.) TC was the adult, he broke the law, shattered many lives (at least temporarily), and needs to be prosecuted. (*Invoking Bentley's mantra from p36, here.) Just another angle I've been considering from the sidelines.