I don't think they have any direct evidence for the language spoken by the creators of the Indus Valley civilization (of which Harappa and Mohenjo-Daro are the most notable centers), but associating them with the later Dravidian languages is a logical guess--the Dravidian family is the largest of the non-Indo-European languages in India.
The way to become famous forever would be to decipher the Indus Valley script. If it were easy it would have been done already.