ISTPs use a combination of investigative skills (wanting to get to the bottom of things using analysis), attentiveness to details, and hunches whenever they solve crimes. Dave fits this profile, since he is always digging after the truth, curious about the motivations of the killer, looking for patterns in his behavior (“he’s gone off his pattern”), and absorbing the crime scene details. He’s also somewhat detached; after two kids see a man murdered, he insists on talking to them, even though their father reminds him that they just had a traumatic experience. (Ti-doms aren’t always aware of the emotional dynamics of a situation or the trauma that other types can experience, because they look at things so clinically.) He has a sense that everything will work out in time, or as he says, “something will shake loose,” and give them the edge they need to make progress on the case. He does a lot of the leg work, tracking things down, talking to people, and trying to piece together the clues, but doesn’t remember the finer details as much as Robert, and doesn’t think in the same way that he does. It doesn’t occur to him, because he didn’t break the code, that the killer might go to the library for the same books Robert wanted, and that that could leave a paper trail (it didn’t; he stole the books rather than checked them out). He also looks for loopholes, so he can give Robert information to build up his case, without technically breaking the law. But when Zodiac stops killing people, Dave moves on to other cases—because he lives in the present. Se cares about what’s right in front of it, and while an old case haunts him, he’s not going to let it distract him from the current cases on his desk. His low emotional awareness makes him agreeable, but not emotional.

Enneagram: 6w5 so/sp

All super-ego types have a sense of “I should” that dictates their behavior, in connection with their responsibility to other people—6s in particular feel responsible for the common good, which comes up when David is talking to Robert about the Zodiac case, several years after the killings and the subsequent phone calls and messages have stopped—it bothers him a lot that he never solved the case, but “a lot of people have gotten murdered since then… and those people’s families need us.” He feels obligated to do what he can to solve crimes, so others can feel safe and have justice. David isn’t one for bucking authority, but he is also willing to bend the rules in the interest of helping people. “I can’t tell you anything,” he says, right before adding that Robert should ask questions of someone, or check out this lead, or we found this during our investigation (off the record). He gives Robert stuff to look into, while he’s investigating other crimes, but also believes that Robert shouldn’t be doing his job (“you’re a cartoonist, not a cop!”), and at one point, decides to stop looking into the case completely (“that’s it; I’m done”). Dave questions things and digs around to get to the bottom of them, trusting his own logic in the process, but also being obedient to the needs of whatever is right in front of him. Unlike Robert, who is a 5 and can get hung up on the past, Dave deals with the present.

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