Gudjonsson (1992; 2003) noted that some suspects believe that their false confession will be found out later on in the criminal justice process and that they will not be wrongfully punished. This type of confession is of interest to investigative interviewing policy makers. Individuals who are particularly susceptible to compliance (for example, people with a learning disability) may be especially vulnerable to this form of false confession.

IMO, this is exactly what was going on with Brendan. When he said "but what if he (SA) says something different (can't recall exact quote atm), I honestly believe with his limited ability to reason through and understand his situation, that he believed if his story was different from Stevens, regardless of what he said, that it would be enough to keep him out of trouble.

Meanwhile, he tells them whatever they are asking him to, just so he can relieve his immediate and substantial discomfort, be done with it and go home like he did after the first two interviews interrogations. His ability to think through all of the steps which would lead to a conclusion about his final outcome was severely limited by his recognized deficits in executive functioning. An issue in that area can leave a person incapable of working out the final outcome of their actions if it involves a series of steps/actions to be taken. To anyone not familiar with this sort of deficit, the end result can look like someone who is just a really bad liar.