This has to be one of the craziest things that I have ever read...this is from NME.com:

According to the News Of The World, the Nirvana frontman's remains – the location of which has previously been kept secret – were taken from the Los Angeles home of his widow Courtney Love.

The ashes were said to have been kept in a "pink teddy bear-shaped bag along with a lock of his hair" and were taken with some jewellery and clothes.

Here is the full text of the NME article on the theft.