Elastic search over an already existing lucene index

I have a system that uses lucene. Now for a few reasons I would like to add a distributed search feature over it.

The question is can I use the existing lucene index created by the IndexWriter of lucene, for searching with elastic search or should I create a new index using ES's IndexWriter. Do note that the Lucene version we have used is 2.3.1. Any help would be appreciated.