In this phone conversation (transcript in link) with his mother (which is not entirely included in the docuseries), Brendan told his mother that he did it, that Steven made him do it, and that Steven had touched him (and others) inappropriately in the past.
Mom: What all happened, what are you talking about?
Brendan: About what Me & Steven did that day,
Mom: What about it?
Brendan: Well, Mike & Mark & Matt came up one day and took another interview with me and said because they think I was lying but so, they said if I come out with it that I would have to go to jail for 90 years.
Mom: What?
Brendan: Ya. But if came out with itT would probably get I dunno about like 20 or less. After the interview they told me if I wanted to say something to her family and said that I was sorry for what I did.
Mom: Then Steven did do it.
Brendan: Ya
Mom: (Mom Crying) Why diddn't you tell me about this?
Brendan. Ya, but they came out wi.th something that was untrue with me
Mom:. What's that?
Brendan: They said that I sold crack
...
Mom: So did you talk to her family?
Brendan: No
M: Huh
Brendan: They just asked me if I wanted to say something to them, on the tape.
Mom: Did you?
Brendan: .lust that I was sorry for what I did.
...
Mom: Did he make you do this?
Brendan: Ya.
Mom: Then why didn't you tell him that.
Brendan: Tell him what
Mom: That Steven made you do it. You know he made you do a lot of things.
Brendan: Ya, I told them that. I even told them about Steven touching me and that.
Mom: What do you mean touching you?
Brendan: He would grab me somewhere where I was uncomfortable.
Mom: Brendan I am your mother.
Brendan. Ya.
Mom: Why didn't you come to me? Why didn't you tell me? Was this all before this happened?
Brendan: What do you mean?
Mom: All before this happened, did he touch you before all this stuff happened to you.
Brendan: Ya.
Mom: Why didn't you come to me, because then he would have been gone then and this wouldn't have happened.
Brendan: Ya ..
Mom: Yes, and you would still be here with me.
Brendan: Yes, Well you know I did it.
Mom: Huh
Brendan. You know he always touched us and that.
Mom: I didn't think there. He used to horse around with you guys.
Brendan: Ya, but you remember he would always do stuff to Brian and that.
Mom: What do you mean.
Brendan: Well he would like fake pumping him
Mom: Goofing around
Brendan: Ya but, like that one time when he was going with what's her name Jessica .. sister. Mom: Teresa?
Brendan: Ya. That one day when she was over, Steven and Blaine and Brian and I was downstairs and Steven was touching her and that.
-- There's no denying that it was unethical as hell for the investigator of Dassey's own attorney to elicit a confession out of Brendan, but the documentary suggests that the investigator peppered Brendan with leading questions and basically fed him the answers. From the full transcript, that is not the case at all. Brendan not only confessed, he gave a very detailed account of what happened. They had sex with Teresa on the bed, then they carried her out to the garage, where they cut her throat, and that's where Steven shot her five times with the .22 Brendan said he pulled from above his bed. Then they threw her in the fire. She begged for her life through the entire ordeal. Brendan even cut off some of her hair. Then they cleaned up with bleach and burned all the clothes in the bonfire.
The bits and pieces from the interview provided in the series make it seem like Brendan is kind of making it up as he goes along or is being fed answers. The 21-page transcript leaves very little doubt of Brendan's role. But again, Brendan's IQ is 70. He'd been molested by Steven in prior occasions. Basically, Steven forced him to do this, and Brendan wasn't bright enough to say no. He's also not bright enough to make up a story that matches much of the evidence, without being fed the answers.
On the other hand, make no mistake: That was tantamount to a coerced confession. From a legal perspective, the information contained within it was worthless. Brendan would've said anything at this point, and it should've never been admitted at trial. Yet, it was, and to any jury seeing it -- and the specificity of the details -- you might see why they believed Avery and Dassey committed the crime.
Sources: Milwaukee Mag, Reddit
