Your poor dh! The male urge to protect his loved ones is as powerful as it is primitive and it defines a man as much as his gender. Your dh was unable to protect his dd when she was in greatest need of his physical strength and the fact that the law has failed her, but he cannot mete out his own form of justice to the youth who perpetrated such a heinous crime on his dd have combined to effectively demasculinise him and he's questioning his very identity, his value to his family, his use to society, his purpose for being.
Encourage him to talk to you about what he'd like to do to the oxygen thief who harmed his dd, allow him to express his fantasies in a open manner and join in with them if you can before very gently reminding him that if he were to act them out, his dd would suffer even more by him being deprived of his liberty - think of this as being an exercise whereby you're trying to implant an almost subliminal message in his brain and repeat it as often as you have patience for.
As I don't know anything about your personalities/state of your marriage/likes/dislikes/hobbies/how much time you spend together etc, the following are some of the strategies I'd adopt - reject any that don't resonate with you:
Think 'invalid' because he needs a period of convalescence to recover from the original and ongoing shock of finding himself to be invalid as in having no legal right or standing to obtain justice for his dd.
Wrap him in a blanket of love, but make it subtle rather than cloying. Buy/cook his favourite foods at least once a week but don't draw his attention to what's on the table -watch to see if he notices and only comment if he does. Use gestures to signify your love for him - greet him with a kiss, put your arms around him momentarily when he's standing still, rest your head on his shoulder if you're sitting on the sofa together.
Use your femininity to counteract the testerone fuelled inner rage he feels at his inabilty to 'do' anything that would ensure the cowardly little shit got/gets his just desserts. Dress with extra care, be slightly flirty/suggestive, give him come hither looks in a light hearted but meaningful way. Use your sexual relationship to reaffirm his manliness; revel in the maleness of him and let him know it.
Turn the tv off and distract him with board/card games, chess, darts, table tennis (if you've got the equipment). Look for articles in the news or books/art that will stimulate debate and, if possible, engage him in a project of some kind which will require him to flex his muscles and serve to tire him out. Tune into Classic FM, work your way through all of Mozart and Chopin's catalogues or listen to jazz/heavy rock/whatever is your bag.
Get him out into the fresh air as often as possible. Plan outings to places you've yet to visit, to timeless places such as rivers, forests, sea shores and to churches, buildings olde worlde inns that are steeped in history. If you can see the night sky from your garden, sit out on any remaining warm evenings and draw his attention to the eternal nature of the stars that have gazed down on this earth since its creation as he needs to establish a philosophy that will confirm his rightful place in the grand scheme of things and enable him to reach an accomodation with his weaknesses as well as his strengths.
Suggest he has a warm bath before bedtime and make him a cup of hot milk with a shot of whisky and a spoonful of sugar to drink in bed. If he continues to have difficulty sleeping, ask in Chat or on the General Health board for recommendations for over the counter products that will give him a good night's sleep, or get a prescription for mild sleepers from his GP. Also give consideration to anti-depressants to tide him over until he can be asssessed for counselling.
Be wary of telling him about the lads that have acted as vigilantes of sorts as it may inspire him to proposition one/all them to hit the fucker in more ways than one. If you intend to do so, present it as 'I heard that shitface got into a scuffle and came off worse - karma works'.
Bad things happen to good people and he needs to repeatedly hear 'it wasn't your fault' and 'there's nothing you could have done to prevent it' just as much as any other victim of serious sexual assault.
I feel so sorry for your dh. I want to give him a big hug and tell him that, although he will never forget the destabilising effect on his perception of himself occasioned by his dd's attacker, he will begin to recover his equilibrium in the not too distant future.
You may find this organisation helpful: www.pandys.org/secondarysurvivors.html