David Fincher's gritty thriller commented on the urban blight and religious conservatism of the Reagan era. But it also predicted our obsession with true crime today.

Thirty years after its release, David Fincher's Seven is now celebrated as the zenith of neo-noir crime thrillers. It raked in a whopping $327m (£250m) at the box office on a $34m (£26m) budget and earned raves from most critics when it came out in 1995. Still, the persistent argument against the film is that it relies too heavily on shock-and-awe gruesomeness to distract from its paper-thin ideas and shopworn crime tropes. A Washington Post critic lambasted Seven for disguising "formulaic writing" with gratuitous "bloodletting", while a New York Times reviewer lamented that "not even bags of body parts… keep it from being dull".

Warning: This article contains descriptions of violence that some may find offensive.

Three decades on, however, it's clear that some critics missed a different layer to the film – namely, how it interpreted the US's social crises of the 1980s. There was a worldwide recession at the start of the decade, and this coincided with high urban crime rates, a crack cocaine epidemic and the spread of Aids. The US's new president, Ronald Reagan, responded to these issues with talk of being "tough on crime", and his high-profile supporters included various influential Christian figures – leaders of what was known as the Christian right or the religious right – who preached the importance of traditional family values.

All of this fed into Seven. On one level, the film is an exquisitely well-made thriller about a psychopathic serial killer, but beneath its noir-style veneer lies a fascinating take on the way the US responded to some of its most divisive social issues.

The film's heady premise is easily unboxed. Two detectives, jaded veteran William Somerset (Morgan Freeman) and quixotic rookie David Mills (Brad Pitt), pursue a polymathic serial killer known as John Doe (Kevin Spacey, stealthily absent from the opening credits) as he orchestrates murders in a symbolic parallel with early Christianity's seven deadly sins. The trail starts with the corpse of an obese man, targeted for the sin of gluttony, whose stomach ruptured after being forced at gunpoint to gorge himself. As the other murders unfold, the detectives flail about without doing much detecting until John Doe inexplicably surrenders himself. The twist comes when Mills discovers what's inside a courier-delivered cardboard box – it's his wife Tracy's (Gwyneth Paltrow) severed head – and in the now iconic climax, he succumbs to the seventh sin of wrath by killing John Doe on the spot.

Unlike the mysterious John Doe, the film does have a traceable origin story. Andrew Kevin Walker wrote the original script across three years in the late 1980s after moving to New York in 1986 and getting a job at Tower Records in the Astoria neighbourhood in the borough of Queens. He'd grown up in the rolling hills of central Pennsylvania, and his immersion in the concrete jungle of New York, then ravaged by crime waves and the crack and Aids epidemics, was a visceral shock.

"Every time you'd walk up a stairwell, the crack vials would crunch underfoot," Walker tells the BBC. "Trash accumulated on the sidewalks, and I realised after a while that I'd become inured to the sounds of gunshots. Across a week, you'd see a car abandoned, then its windows smashed and tyres stripped, and by Saturday it'd be a burnt skeleton. It felt like an external blight that eventually seeped into your soul and hollowed you out."

These may just have been Walker's own personal impressions, but reports from the time show that urban crime was on the increase: a........

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