Hi,
please, put your Moderator in a special group, for example, Moderators ( I guess he is already there ).
Search for the macro "can_delete" and edit it like this:
<override_macro name="can_delete" requires="user" dot_parameter="node_attr">
<n.either>
<condition1.both condition1="[n.not.is_banned/]" condition2="[n.owns.node_attr/]"/>
<condition2.is_in_group group="Grupo" />
</n.either>
</override_macro>
To delete a single message he should use "Delete this post" or "Delete this post and replies" when he wants to delete the whole topic.