Hence the colorfully named Fixated Persons Investigations Unit, which the New South Wales police announced last month. It’s intended to find people like Mr. Jabar and prevent them from radicalizing fully.

But “police unit” might be a misleading description. In fact, it is a partnership between the N.S.W. police and the health department that, rather than arresting suspects, is more likely to take tips and send the people concerned to a mental health professional.

The rationale, as the N.S.W. police commissioner, Mick Fuller, explained, is that “in about 80 percent of cases” of lone wolves like Mr. Jabar, “a family member or a friend noticed a significant change but didn’t have the confidence to call anyone to report it.” The idea is that this will change if when “you call and say, ‘Look, I’m concerned about my son,’ police are not going to come through the door with a sledgehammer.”

This is remarkable for the admission it makes: Terrorism has outgrown the ability of law enforcement, and if the state is going to keep up, it will need to incorporate something akin to a pastoral role. That, to be sure, is a radically countercultural approach — something you could hardly imagine hearing from a politician — but it is born of years of research and bitter experience.

In Australia’s case, the plan has the advantage of borrowing from Britain’s experience with its Fixated Threat Assessment Center, which has been running since 2006. That center was created not to find terrorists but to find people with obsessive, stalker-like fixations on public figures — especially politicians and the royal family. Such people overwhelmingly suffer some form of mental illness, particularly psychosis, hence the partnership with the health department.

Can you extrapolate this to terrorism? Only if you assume there is something about lone-wolf terrorism that is qualitatively different from the more networked, group-based version that has dominated terrorism’s history. That history shows that terrorists only rarely suffer from any kind of personality disorder or psychological condition, which is why the search for the “terrorist personality” has proved fruitless and been discredited.