We have seen Nexus 5 leaks before and we will see more leaks before it is finally released to the public. The latest leak is the clearest you can get now, it is a 7-minute video walkthrough of the next Google Nexus smartphone. The video appears to be coming from smartphones.sfr.fr.
The Nexus 5 in the video appears to be running on KeyLimePie, that is the name Google gave it before finalizing KitKat, so it might be running a older build of the OS. Also there is no Nexus branding on the back of the device as we have seen it in previous leaks. But by the time it launches in the market things will change a lot.