[Manga] Shingeki no Kyojin - Page 8

The armored titan is Reiner Braun. Of course, allow me to demonstrate why I think so.

1. Physical Appearance
First, obviously, is their appearance. Here is a link to chapter 2, page 30, to see what that titan looks like:
http://www.mangafox.com/manga/shinge...1/c002/30.html

And compare it with Reiner's appearance:
http://www.mangafox.com/manga/shinge...1/c002/38.html
So, at the very least, they look very similar, which is a prerequisite.

2. Circumstantial Evidence
Here, I have a few incidents to offer as evidence. They are by no mean conclusive by themselves, but they give you hints. Big hints.
First, the most insignificant of hints: he's still alive. I know it doesn't mean much, but it IS significant. While almost everyone else has died, he still lives, and is therefore someone worth considering as a candidate.
Now, go back to chapter 7, page 11. Here, it's clear that Annie and Reiner have some kind of unique, special relationship. Here she asks HIM specifically: "What now, Reiner?" To which he answers: "Not yet... Let them gather first." Now, the assumption here is that he's talking about the titans. In other words, he says that they should let the titans gather first before acting. But if you think about it, that makes no sense. If they actually let more titans gather around the tower, they'd have LESS of a chance to rescue the others. With more titans gathered, it would be even MORE difficult to do anything. Because, remember, a the time, he and Annie don't yet know about Eren's titan power. My hypothesis here is that he ISN'T actually talking about the titans; he's talking about the HUMANS. He's telling Annie that they should let the humans gather a bit more before acting. What did he and Annie have in mind? Well, actually, Armin reveals it in chapter 27 page 7. They were waiting for an opportunity for Reiner to change into his armored titan form and bust through the next wall's door. But their plan is ruined when Mikasa appears and rallies everyone to attack the tower. Now he and Annie are forced to participate and help out the humans. Once that happens, on page 19 he even says: "Didn't see that one coming..." And you can even tell that Annie looks like she's caught in a situation she can't get out of and seems frustrated by it. Later on, as Armin explains in chapter 27 page 7, they find out about Eren's transformation, and that changes their priority from destroying the door to focusing on Eren.
Next, go to chapter 9, page 6. They're inside the tower and everyone has been told that there's a titan going wild on its own kind, but they don't know that it's Eren yet. Here, Armin asserts that this titan is stronger than the others and that things will be OK. Then check out the question that Reiner asks him: "Just how much do you know about that titan?" I know that it's not clear, but my impression here is that Reiner himself knows why there's a titan doing this crazy, unexpected stuff. He seems to KNOW what's going on. And he's wondering whether Armin does too. He wants to know whether Armin has figured something out about that titan. Anyway, his question here is clearly suspicious if you think about it from a hindsight's point of view.
Next, to emphasize the special relationship he has with Annie, go to chapter 9 page 21. Here, they just killed the smallish titans inside the tower, and you see that Reiner says to Annie: "That was a close call, Annie... I'm really glad to see you're unharmed..." There's definitely something going on between those two...
Next, before they flee, they go to the roof of the tower, and once again, Reiner says something strange. He insists that they should save the anomalous titan. He says they need it alive! And guess who backs him up? Annie! She says: "This titan might turn out to be an ally." Do you get it? Annie and Reiner are both the same as that titan, so they really want to make sure the person inside stays alive because it might be one more person who they could add to their side. This is also possibly foreshadowing the reason why later Annie, in her Titan form, goes after Eren so relentlessly. She and Reiner definitely want him on their side, for whatever reason.
Next, go to chapter 11 page 10. Here Reiner is the first one to realize that the smoke is titan vapor and that something is going on. So he immediately goes in that direction. Who follows him immediately? Annie, of course...
Next, go to chapter 15, page 21 and younger Eren is talking about the first time the colossal titan attacked. When he mentions the armored titan, who does the author happen to show in that panel? Do I even need to say it? Reiner, of course... The author is giving us some pretty big hints. We just have to pay attention to them.
The next hint is a HUGE one. It happens in chapter 16 page 16. Here Eren was originally looking for advice on how to maneuver in the air properly and ended up talking to Reiner and Bertholdt. Here, Bertholdt starts to talk about where he and Reiner are from, and what happened when the colossal titan showed up on that fateful day. On page 17, he says "After that... I don't remember much... (...) We took our horses and fled all the way to wall Shina". Did you ever think that this story was kind of strange? When I first read it, it seemed really weird that he wouldn't remember how he got to safety, but didn't think much of it. But now that I've read it again, I'm 100% sure that he's lying there. That's not what happened to him that day. He and Reiner were not in their village that day. Obviously Reiner is the armored titan. So who does that make Bertholdt? You guessed it: the colossal titan. Think about it. It fits: he's tall, quiet, and we never see him much. But he's alive. I don't have enough evidence to claim it for sure right now, but believe me, he is the colossal titan. If you think otherwise, let me know why. Anyway, back to the story. Check out what Reiner says after Bertholdt tells his story: "Jeez... What possessed you to start blurting out that story like that?" and Bertholdt immediately apologizes. Why? Because he totally made that story up, and of course, Reiner knows it. So Reiner is scolding him for making it up because he probably thinks that it might blow their cover someday if anyone ever finds out that he lied about it. In other words, Reiner is mad that Bertholdt just "blurted out" a random story like that, knowing it could put them both in trouble. Then check out what happens next. Bertholdt goes on a rant about humans and society's expectations, etc. He's definitely weird and has issues with humans. Basically, he's definitely the colossal titan. And then, look what happens next. Reiner says "I got something too. Something I'll never deviate from... There's no going back." He's talking about his secret. Or I should say their secret: him, Annie, and Bertholdt. That whole thing about seeing his hometown again is just a side wish. Just something he also wants to do, beside his "titan mission." Especially look at his eyes when he says "I'll do it. No matter what it takes." If you reread this entire conversation with the fact that he is a titan in mind, then you see it completely differently...
All right, if you're still not convinced after ALL that, then this is it. This is the big one. This one is UNMISTAKEABLE. IF YOU DIDN'T READ ANYTHING ABOVE, THEN READ THIS ONE. Now this time, start with the assumption that Reiner is the armored titan. Now go to chapter 23 page 15. Here Armin, Reiner and Jean are chasing after the female titan (Annie). Armin explains that she's most likely after Eren. And here we find out that Reiner thought that Eren was in the right flank because his plan said so. Of couse, that wasn't the case, since people had been given false info. But guess where Annie had come from? That's right, the right flank. That's because he's the one who told her. So once they figure out that they've been given wrong info, Reiner wants to know where Eren really is so he asks Armin. Armin tells him where he thinks Eren is, and it turns out that he's right. So then they attack Annie. Annie makes Armin fall off his horse, but doesn't kill him. At this point, Armin figures out who she is. The proof that he knows at this point is that just when she's about to kill Jean, Armin yells out his name. Armin knows that Annie knows Jean and that she would definitely hesitate to kill him. While Jean thinks that Armin has lost his mind, he's actually doing it on purpose to save him. And guess what? It works! Annie freezes up and doesn't kill Jean, who is very surprised by this, but thankful for his life. But then, what does Reiner do? He acts like he's going for the neck of Annie, when, in fact, he would have had ZERO chance of succeeding, and he should have known as much. So, this time, think about it from his point of view. He told Annie that Eren was in the right flank, but they both found out he wasn't (By the way, this is why Annie was lifting up their hoods, looking for Eren in the right flank) there. But now he's found out where Eren REALLY is from Armin, so he needs to somehow relay this information to Annie. So what does he do? He pretends to attack her and go for her neck. But what really happened is that she caught him and (mysteriously) brought him up to her ear!! While it looks like she killed him, he's actually taking the opportunity to tell her where Eren is! Then he gets out of her hand, all bloodied, and picks up Armin. He makes up the excuse that they've done enough, but that's actually so that they won't bother her anymore, now that she knows where Eren is. So what happens? Annie immediately gets up and runs in Eren's direction. Armin notices this, while Reiner tries to pretend that she's running away. One last thing: Annie really did hurt Reiner when she caught him in her hand and somewhat crushed him. So notice what is coming off of Reiner's body as he's getting away from her... Yeah, you guessed it: titan vapor!! His wounds are healing! Look at how bloody he was getting out of her hand, and then a few seconds later he's running away with Armin under his arm like nothing happened, while the entire time vapor is coming off his body. And trust me, it's not her vapor, it's his.

Source: http://forums.mangafox.me/threads/367305-I-know-who-the-armored-and-colossal-titans-are...?highlight=Shingeki no Kyojin

Eren's entire squad got eaten and his leg needs to be amputated if he can even escape(probably will)