People who own the guns should be liable for criminal & civil lawsuits and criminal MANDATORY jail time penalties for being the last legal owner of any gun used in a crime. You own it, you prevent it from getting out into the criminal world.
In DC v. Heller (2010) the ruled against regulations that required people to store their weapons in a disassembled state and bound by a trigger lock. I think they would also rule against requiring guns to be stored in a locked cabinet. You can not have laws that limit the effectiveness of weapons as part of self defense.
There has to be some form of culpability where someone is found to be negligent. Simply having their weapon stolen should not be grounds for jail time, nor should they be sent away for lawfully selling their gun under the correct regulations.
We can use cars as an analogy. If a car dealer sells a car without knowing that it will be used in a crime then they are not held liable. If someone has their car stolen they are not held liable for the crimes that the thieves commit while using that car. However, if you supply a car knowing that it will be used in a crime, or illegally sell a car to people you know are criminals, then you are in deep trouble. The same should apply to guns. We should be able to trace guns from birth to grave for this very purpose.
Edited by Taq, : No reason given.