The Computer Owner - Guilty or Not Guilty?

Von-at-Infosec_Writers asks: "It is relatively easy to trace a hack back to a particular computer, but proving that a specific person committed the crime could become much more difficult especially since, as a recent CNN.com article stated, a hacker's legal defense can be: it wasn't me but my hijacked computer that committed the crime. 'In some cases, I do suspect there are people whose computer is taken over by third parties. It's also a clever defense to exculpate your client,' says Michael Allison of the Internet Crimes Group.What are possibilities to overcome this problem; to prove that the computer owner, without a doubt, is in fact responsible or not responsible for the crime?" As computers become more and more prevalent in our infrastructure, the consequences for computer crime become that much more serious. How much responsibility does the owner of an Internet-connected computer have for crimes committed using their equipment, and what are ways we can best determine their involvement, or lack of it, in said crimes?