Interesting case and some really good advice. I'm glad that things are now kind of normal and have been worked out, but I think I need to address an important issue that was being discussed in this conversation.
Level of Tolerance in Organizations
The issue was "what is the level of tolerance that any organization - big or small, should exhibit towards their employees - probationary or permanent, when it comes to gross misuse/abuse of the system or indiscipline."
Has the extension of the probation period actually solved the core issue, or has it just allowed the fire to cool down and given everyone some breathing time before a similar fire starts again? Ideally, the employee should have been asked to leave immediately. Since you had all the proof and relevant information, asking him/her to leave would have been valid.
Setting an Example
Why am I proposing such drastic action? Because sometimes you need to set an example for the message to go across the organization. Sometimes you need to be a "bad guy" to ensure "good" for your organization. Tolerance is good... at the right place and with the right person.
A person on probation is just starting their relationship with you. Everyone tries to create their niche in the organization at this time. If a person is doing anything that is not in any way helping them build their relationship within the organization, believe me, 99% of the time the person is not staying there for long. They are just there for the ride! Do they deserve the tolerance? Definitely not!
Of course, this would have been different for a person with more history in the organization. But then that's my way of looking at it... ;-)
Cheers,
Navneet