Test case:

• enter https://repository.jboss.org/nexus/content/groups/public/org/picketbox/picketbox/4.0.6.Beta2/picketbox-4.0.6.Beta2.jar.sha1
  You will get sha1 for the org.picketbox:picketbox:4.0.6-Beta2 artifact (2b969e8e524c174b510819118e283bcf9d5479e2)
• enter https://repository.jboss.org/nexus/service/local/data_index?sha1=2b969e8e524c174b510819118e283bcf9d5479e2

You will get:
<search-results>
<totalCount>0</totalCount>
<from>-1</from>
<count>-1</count>
<tooManyResults>false</tooManyResults>
<data/>
</search-results>

which is a wrong result because the artifact exists.
A GAV query returns the correct result. For instance:
https://repository.jboss.org/nexus/service/local/data_index?a=picketbox&v=4.0.6.Beta2
returns the correct result.

The JBoss Source Lookup plugin (https://community.jboss.org/community/tools/blog/2012/01/24/jboss-source-lookup) requires a sha1 query.