Why/How can Arno see his victim's memories?

Perhaps I missed something important, but, is it ever explained why/how can Arno see the memories of the people he kills?

At the end, he even speaks with Germain (consciousness?).

This is the best description I managed to find about it:

(No, they are not my words, it's merely a post that I found that had the best description and summary of what is happening)

Ugh... It's called Psychometry.

It's tied to the Sixth Sense from the Precursor (First Civ) race. Part of the Assassin training is coaxing that ability out through years of practice, only a small number of humans DON'T have the capacity for it, but even fewer can do it as naturally as the playable characters can.

All of the confessions we've seen are a form of that sixth sense, Unity just changed how it was displayed to the player. They were initially shown as White Rooms (literal term for them given by Ubisoft) because the Animus could not render the information it was given for those specific memories, but Helix is a vastly more powerful device that is finally capable of doing so. Plus Arno tapped into his Sixth Sense (Knowledge) differently. He's arguably the most well trained in this area than the past characters. He's capable of simply looking at a fortified area and using this sense to detect weak points. None of the other characters could do this, or if they could Ubisoft never elaborated on it until now. The sixth sense allows the user to see the emotions and intentions of those around them, and if trained well enough, allow them to see directly into the mind of someone they're touching. The limitation to that, however, is that they can only see what the person is thinking and nothing else. They can't actively scan that person's mind to specific information, they can only view what is being given to them. Hence why Arno does it as he kills them, so he can see events that flash before the target's eyes.

• ry_mann, http://www.gamefaqs.com/boards/772633-assassins-creed-unity/70597492?page=1#15