A thief stole something which injured him. Is he liable for his own injury? Let's say it was a stolen gun. Would the man who loaded the gun bear any responsibility for the thief's injury?
The basic cause of having to pay for damage caused by your property is if you were negligent in gaurding it from causing damage (Bava Kama 9b).
Since the owner of the gun was not negligent he bears no responsibility for the thief's injury.
Further, if the gun now injured someone else the thief would be responsible as he has removed the safegaurds made by the owner.
when someone breaks into someone else's house they are violating that person's fundamental rights to life (b/c doing so is a threat), privacy, and property. When someone acts in such a callus manner they loose their own rights and any injury incurred while stealing is on the thief and the thief alone
source: If a man comes to kill you, rise first and kill him first (Talmud Brachos 58a) Without great personal risk it is difficult to determine whether a thief is only there to steal, was planning on other physical harm, or will react violently to being caught in the act.
As far as a thief who injures himself from stealing he would not have injured himself if he didn't put himself in the position of trying to steal from this persons house. So how could you possibly say anyone other than himself is responsible for his injury?