The conventional interpretation of his occupation might have been investigator. Marty Marias was more accurately contracted as an observer, and therefore a consultant; he reported back to others what he saw, and as such was an interpreter.
Marty had recently been asked to talk about three particular individuals, all of whom who had been taken into police custody and had been subjected to interrogations. They were persons of interest in the assassination of Gabriel Bell. He wasn't given their complete identities, and in truth he preferred it that way.
The first of them was a woman known as Zinn, a transient and amnesiac who had been taken in by another of them. In her case, Marty was only interested in her details, her particulars, what her information told him about whether or not she would have been capable of killing a man. She had first been identified as homeless, but that quickly turned out not to be the case. She had been the victim of an assault, and so that was how she had ended up in the general area of the crime, disoriented and "rescued" by one of the others. She was a school teacher, in fact, and had only been missing a few days when she resurfaced and became intwined in the sequence of events that led to the death of Gabriel Bell. She taught first grade, children who had reached the age of dawning responsibility. Marty saw that she was not comfortable in her life, that she would have done anything to escape it, but not in conjunction with the assault, not with the loss of her self-control. If anything, she would have used the preceding events as a frantic means to rediscover herself, to a semblance of what she had once known about herself.
The second was a writer, whom Marty knew as Jake, no last name, just as the others had not come with given names, or so Marty had to assume. Jake was clearly unfulfilled in his life, possibly disgruntled in his frustrations to make a career out of his stories, and it was written all over his face. Given half a chance at even a suggestion of acceptance, he would have done anything, would have been capable of anything, would have rationalized any act, no matter how extreme, if the circumstances presented themselves. Marty could easily extrapolate from any of that Jake's ability to kill, especially someone who had achieved a measure of success and in a public way that he himself had been denied, or had denied himself (it was never easy to tell which one).
The third, and the man who had affected the "rescue" of Zinn, was called Swift, and he had come into the scenario under very ambiguous circumstances, and had not adequately reconciled them for himself even though he had taken great strides in the attemot. It was Swift who had mistakenly identified Zinn as homeless, and, intoxicated by her not-inconsiderable beauty, had taken it upon himself to free her from the sorry mess that had become her life. He was a businessman, who was already familiar with the allure of power, who would have relished whatever fantasies he had constructed around the figure of Zinn. Once the realities were made plain, he had attempted to redirect his efforts, so that he would not become impotent in her eyes, and would retain the illusion of control he had once enjoyed over her. Such a man would easily have been capable of switching this sense of identity into other, less wholesome, directions, if it had proved to be a waste of his time.
Marty considered the context these figures had found themselves in, the desperation they had all fallen into, and the atmosphere of despair and resolve that created such a dangerous situation, even before the murder of a prominent individual like Gabriel Bell. Although he had ruled out the woman already, he felt that anyone might have been driven to that point, even beyond their normal limitations, because they had been drawn to that place by a common desire, something that had previously been elusive for each of them, but had crystalized in a single movement, and now in a single death. Those others who had observed that place tended to remark that such individuals were hardly worth their pity, that if they had simply worked out their own problems, they wouldn't have had to blame someone else.
The death of Gabriel Bell had galvanized the entire movement, forced those observers to view the plight of the individuals who had gathered in a new light. Just as Marty was charged with scrutinizing three individuals, an entire nation was now forced to re-evaluate their judgments. Bell had been a charismatic victim, and that was all any such movement ultimately needed. Marty wondered if the solution to his problem were similar. It wasn't so much what any of them had to gain, but what the murder of another person would mean to them personally. The woman wouldn't gain anything, obviously, but a murder, even a misguided and misdirected one, would give her back the power she'd lost. The same would be true of the businessman. The writer could only be accused by way of a psychotic break. Although he would surely have had a kind of motive, his personality otherwise contradicted such an outcome. He was an introvert by choice, not by nature. Although he would have suffered from the misdiagnosed social reactions of others most of his life, he was ultimately an observer, much like Marty himself. To call the writer a killer would have been for Marty to call himself one. The woman was much the same; anyone who worked with children inherently considered life in their own way sacred. She couldn't have been the killer anymore than she could have killed the businessman for taking advantage of her, or at least having the appearance of having done so. The businessman, however, and not because he was a businessman or because business itself was inherently antisocial or that he would have had a personal grudge against Gabriel Bell as someone who had spoken out very publically against some of the very practices the businessman himself had depended on throughout his career, but because of the rejection of the woman, of the contradiction he couldn't reconcile, and so he took it out not on the woman, but Gabriel Bell, someone in whom the businessman could project his feelings of inadequacy.
So that was how Marty reported it to those who had asked his opinion.