You might need to give the timeline query param as well in addition to the expand query param which is required. By default, if the timeline query param is not provided the API is going to retrieve all the audit entries for just today.
You can also get more details on this API including the various query params in the following doc :
http://apigee.com/docs/api/audits-0
You can directly query on this doc page itself and provide the various query params that is valid for your scenario and explanation of each.
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