1) The graph description code in includes/definitions/graph_types.inc.php from September 2014 : 

   http://postman.memetic.org/pipermail/observium-svn/2014-September/007806.html

   http://postman.memetic.org/pipermail/observium-svn/2014-September/007805.html

(and many more commits since)

2) This commit from April 3rd 2015, most notably the changes to includes/definitions.inc.php :

   https://github.com/librenms/librenms/commit/ac4eba78e48362d6d64e4695afb849d6d7ec531e

3) [private]

4) He's one of your users, I assume you know to contact him!  
(https://github.com/laf) [https://github.com/laf)] :)

5) I have a good faith belief that use of the copyrighted materials
described above on the infringing web pages is not authorized by the
copyright owner, or its agent, or the law.

6) I swear, under penalty of perjury, that the information in this
notification is accurate and that I am the copyright owner, or am
authorized to act on behalf of the owner, of an exclusive right that is
allegedly infringed.

7) :

[private]  
Observium  
[private]

In this instance there's no possibility of use the excuse that the code was copied from elsewhere, since I invented the description format myself.

This would make the entire commit an infringing derivative work, since it has clearly been written using our code as a reference.

Thanks!