First your search command is fine.
Setting can_delete will allow you to delete. (Make sure you remove can_delete when you are done.)
Anything is possible with permissions but it is likely good if you are indexing data into the index
We do not have write/read permissions in our roles, splunkd writes, you read, unless you set can_delete. The roles can restrict the index you are allowed to use but you said your search returns events so you are good there.
Are your indexers clustered?
See this section in the link below: "The delete operation and indexer clusters"
http://docs.splunk.com/Documentation/Splunk/6.4.1/Indexer/RemovedatafromSplunk
As already mentioned, check splunkd.log for errors
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