Delete by query range

I want to delete a set of document that fall within a timestamp range.

This delete fails:

curl -XDELETE 'http://search.server.com:9200/ion/_query' -d ' { "range" : { "timestamp" : { "from" : "2011-07-22T07:00:45.012Z", "to" : null, "include_lower" : true, "include_upper": true } } } ';

However, this get succeeds in returning results:

curl -XGET http://search.server.com:9200/ion/_search?pretty=true -d ' { "query" : { "range" : { "timestamp" : { "from" : "2011-07-22T07:00:45.012Z", "to" : null } } } } '

What am I missing here?

Thanks.