Leila Marino

Leila Marino is a person who did business with Abstergo Industries prior to Desmond Miles's arrival. She died under mysterious circumstances. It is also said that she had a romance with subject 16 and might have also been a close friend to Lucy.  

In Lucy Stillman's emails, she asks Vidic about Leila a lot. The only explanation she can get is "she killed herself." This hints at the possibility that she was an assassin and was silenced by Abstergo. Another theory is that Subject 16 killed her and used her blood to draw the symbols all over the animus room. There is also the theory that she and Subject 16 became involved and committed suicide together in order to leave the glyphs written in blood, but this theory is unlikely  since Leila died in 2007, while Subject 16 was held captive shortly before Desmond. But these are just a few of many possbilities.

In the email mentioning her relation ship with "Neumann" Vidic says "Don't dip your pen in the company ink," which would contradict the theory that Neumann is Subject 16.