Well, its not the only time Data 'lied' or was intentionally vague, isn't it?
What about the episode, 'Clues'? Not only did Data intentionally lie, but disobeyed orders.
So, it is within his character do act like this, so as long as he has a a reason that is justifiable, according to Data.
Right before he was transported, Data even
says "I cannot permit this to continue." Permit
what to continue? The endless cycle of Fajo killing people in order for his new play toy to obey? That seems to be what Data was talking about.
Even if Data did 'murder' Fajo, who kidnapped him, incidentally, he would not have faced a Starfleet court-martial. If Worf can go on the lam and kill the man who murdered his wife out of pure vengeance (Episode: Reunion) and only get a reprimand, I don't see Data getting a court martial for 'Escaping his captive by any means necessary.'
"Data has emotions and we don't, therefore what we would do is irrelevant?
" - Quote from poster.
You point out a difference between Data as an Android, and us as Humans, that Data does NOT have feelings or emotions. However, we do understand, and it HAS been established, that Data feels he has rights, ("The Measure Of A Man"), and he does have feelings, like he did with Tasha Yar. Data even hesitated to respond about Tasha about his feelings for that episode, saying that he, "Gave his word."
I suppose that an android in a court-martial, since he is bound by Starfleet oath to answer any and all questions at a court-martial efficiently and forthcoming, without hesitation?

(No, not really.)
The truth is, Data
did have feelings, as early as Season 1. They may not be feelings that you or I feel, its more like a wet sponge absorbing the rudimentary aspects of it.
Look, Data had every intention to fire on Fajo. A hear a lot of people about, "
Well, why didn't he just throw the phaser at Fajor and knocked him out? Even though Data is an amazing machine, he is not infalliable. For example, in "The Royale", the first two times Data threw the Dice on the table, he did not throw a seven or eleven.
Data is surveying the options while Fajo is giving his taunting speech. He could throw the Varon-T disuptor at Fajo, but there
is a chance he could miss. What if Fajo managed to get out of the way? Data threw away his only method of defense and protection. The probability of success is less likely doing that than simply killing Fajo.
Fajo has demonstrated that he would kill people on a whim if Data does not obey his orders. Data is self-aware of his rights, and is aware of his duties as a Starfleet officer. In order to prevent Fajo from killing more people, AND to allow Data to return to Starfleet, the only logical recourse would be to kill Fajo.