I'll get a little lawyery here but just because it's kind of a fun topic. The issue isn't criminal liability, it's tort liability. The homeowner/trapper can be sued successfully only if the burglar can show that he failed to perform a duty the homeowner owed the burglar. For most categories of people on your property, you have at least a duty to warn them of dangers. That isn't true of trespassers. The only duty you owe them is not to intentionally set booby traps. To prove criminal liability, the prosecutor would have to prove the intent to trap the burglar beyond a reasonable doubt, but in a torts case, the burglar would only have to prove it by a preponderance of the evidence. The jury could definitely infer the trapper's intent from the unlikeliness of his explanation as to why all these traps were set on the floor.