Carelessness and stupidity
At this stage, any half intelligent idiot who wants to do anything nefarious on the has several options for messing up their tracks.
1. Crack a handy WEP network in any built-up area (although with the amount of networks without any security whatsoever- why bother).
2. Use IP ghosting and MAC ghosting (particularly easy if you're using a nice little firewall that runs a Linux kernel as its o/s).
3. Bootable memory keys on public access machines
4. Cloning (particularly if you want to frame someone else).
5- I could go on and on.......
Its not difficult to cover your tracks- even if your tracks do eventually lead to someone else. Its also not difficult to blame some of the above if you do get sloppy and get caught- but in practice, the more outlandish the explanation- the more likely it is to be impossible to disprove it (or the more trouble someone will have to go to, to disprove it).
It was unfortunate that the poor Indian guy got over 7 weeks in jail, Airtel should have made sure that the police were aware of the possible problems with the data though- before it was acted on. Then again- Google should never have handed over the IP data in the first place. I'm never going to use Airtel again when I'm in India- think I'll move over to Idea or another of their competitors next time.......