In 2006 a man walked into an internet cafe in Kassel, Germany, and shot dead Halit Yozgat, a 21-year-old member of the Turkish-German family who owned it. It was the ninth in a series of racist killings by neo-Nazis, the motivation for which the police persistently refused to admit. A striking fact of Yozgat’s murder was that Andreas Temme, an intelligence agent for the state of Hessen, was in the cafe at the time, logged on to a dating website in a back room. If there’s one thing a secret agent should be able to do, you might have thought, it would be to notice a killing in the next room, but Temme claimed he did not.

He took part in a police video reconstruction in which he is seen placing his payment for his internet access on the reception table, unaware of the corpse on the floor behind it. His story didn’t seem likely, but in the absence of further evidence it seemed that he would have to be taken at his word. That might have been that, were it not that Forensic Architecture investigated the case and exhibited their findings at the 2017 edition of Documenta, Kassel’s five-yearly art fair. Through creating a full-scale mock-up of the cafe interior, and analysing the sound of the two shots (loud enough, even with a silencer), the dispersal of their smoke and the sightlines of the agent – a tall man – as he put money on the table behind which the young victim was sprawled, it was demonstrated that Temme could not possibly have failed to hear, smell and see the crime.

Forensic Architecture, whose work is going on show next month at the Institute of Contemporary Arts in London, is an agency based at Goldsmiths, University of London. The organisation’s founder and director is Eyal Weizman, a British-Israeli architect. Its primary mission is research, to “develop evidentiary systems in relation to specific cases”; in so doing, it acts as “an architectural detective agency”, working with NGOs and human rights lawyers to uncover facts that confound the stories told by police, military, states and corporations. “We think that architects need to be public figures,” says Weizman. “They should take positions, whatever they do. We map the most extreme and violent forms.”

A bomb cloud is everything a building was in gas form: plaster, concrete, wood, flesh. It’s horrible, devilish dust Eyal Weizman

“We’re building a new sub-discipline of architecture,” he adds. “We just have to figure it out.” They use whatever means they can to reconstruct a hybrid of physical and virtual space – the metadata surrounding phone calls and phone-camera videos, meteorology, eyewitness accounts, reconstructions. They might scrape thousands of images of a bombing off social media and match them with material facts to fix facts in space and time, as if with the coordinates of a multidimensional map. They learn from ancient as well as modern methods, such as the memorising techniques of Roman orators and Elizabethan actors, when helping ex-prisoners reconstruct the monstrous and secret prison of Saydnaya in Syria.

They are engaged in a game of wits with military and security services. Their arena is shaped by surveillance and data collection – factors that give rise to well-founded fears that they might be abused by power. Forensic Architecture aims to make these techniques benefit rather than harm human rights. In a world saturated by images, where seemingly almost everything is exposed to view, they try to make visible those things that are kept hidden. They prefer to call their activity “counter-forensics”, “forensics” being “the art of the police”.

The material is harrowing: to see, for example, from several CCTV camera positions, the daily life of an Aleppo hospital in the seconds before it is obliterated by pro-regime forces. “You never get used to it,” says Weizman. The work is also compelling, both in the inventiveness, precision and patience of the processes and the crystalline outcomes. It might take a year to reconstruct a day, as it did with the events of Black Friday, 1 August 2014, when 2,000 Israeli bombs, missiles and shells were dropped on the city of Rafah, in the Gaza strip. But Forensic Architecture’s research into that day contributed to the cancellation of the “Hannibal Directive”, a classified policy whereby the Israeli military might kill their own soldiers if they are taken prisoner, rather than allow them to become hostages.

This is not the point where most architecture students expect to end up. After studying at the Architectural Association in London, Weizman set up a practice in a conventional enough way for young architects in Tel Aviv. What changed everything was his decision to do a PhD on the ways in which town planning in the occupied territories was used to divide and suppress. “I was trying to show that there could be human rights violation by architecture and planning,” he says, “and that architects can be complicit.”

Forensic Architecture’s reconstruction of the abduction of 43 students in Iguala, Mexico in 2014. Photograph: Forensic Architecture

Asked to contribute to an exhibit of young Israeli architects in Berlin in 2002, he presented a show on settlements, which led to the Israel Association of United Architects cancelling the exhibition and destroying the catalogues. Like much censorship, it made the name of its target, and that year Weizman managed to exhibit his work at the Israeli pavilion in the Venice architecture biennale. From there he “accelerated from the slow violence of architecture and planning” to the rapid violence of warfare and displacement. He founded Forensic Architecture in 2011, their “expertise gradually growing” since. Their areas of interest expanded beyond Israel and Palestine to wherever they might be needed: Kassel, Syria, the disappearance of students in Iguala in Mexico, a lethal factory fire in Karachi, a detention centre in Cameroon where torture and executions took place with the apparent connivance of US personnel based there.

They are “on the side of civil society” and won’t take commissions from government or corporations, but don’t take political sides. Which has given them a wide range of enemies and detractors who, while not equivalent in the outrageousness of their regimes, have some attitudes in common. Forensic Architecture have been dismissed by Germany’s ruling CDU party as factually challenged artists, by Assad as Qatari stooges, by the Kremlin-backed RT TV network as supporters of Islamic State. In Israel they get called “Pallywood”, as in Palestinian Hollywood. “The bastards’ last line of defence is to call it ‘fake news’,” says Weizman. “The minute they revert to this argument is when they’ve lost all the others.”

It is indeed notable that Forensic Architecture use arts venues such as Documenta and the ICA among their means of getting their messages out. This might seem a bit dilettante, in relation to the hard facts of human rights disputes and war crimes cases, but Weizman argues that the means of representation, the ways in which research is communicated to the public, are vital. The proof is in Forensic Architecture’s work, which stands up in court, gets ministers to recant their previous statements, and changes lives and, sometimes, policy. Their theoretical explorations seem to help rather than hinder the factual aspects of their work.

A reconstruction of the altercation of search and rescue operations in the central Mediterranean on 6 November 2017. Photograph: Forensic Oceanography and Forensic Architecture

Weizman also still considers Forensic’s activities to be a way of practising architecture, wielding the profession’s potential for synthesising the contributions of multiple other disciplines. He is quick to pay tribute to the affiliated research project Forensic Oceanography, who investigated with Forensic Architecture claims that NGOs rescuing migrants off the coast of Libya were colluding with people smugglers. Forensic Architecture’s work might require knowledge of the law or munitions, on which they collaborate with the appropriate experts. Members of the agency who are not architects include an investigative journalist, a programmer, a film-maker and a preservationist.

They borrow from the speculative end of the architectural profession, with surprisingly useful results. An example is parametricism, a fad that swept through architecture schools in the first decade of this millennium, which tried to design buildings by feeding data into sophisticated software that then generated exotic but intractable forms. “As a design strategy,” says Weizman, “parametricism is futile and decorative.” Forensic Architecure instead applied its techniques to analysing the clouds caused by the bombing of Rafah.

Forensic Architecture founder and director Eyal Weizman. Photograph: Justin Tallis/AFP/Getty Images

“A bomb cloud is everything a building was,” he says, “in gas form: plaster, concrete, wood, flesh. It’s horrible, horrible, devilish dust.” But you can “reconstruct its force fields out of its form”. Every cloud has a “fingerprint”, a moving one, which means you can pinpoint the place and time from which a photograph was taken from the shape of the cloud. By triangulating and coordinating all the information thus gained, Forensic Architecture could locate particularly large and lethal explosions. They could also calculate the dimensions of the bombs – and hence their weight of explosives – caught in one of the photographs before they hit.

In Rafah their evidence made a convincing case that the object of the onslaught was to kill an Israeli officer who had been captured that morning, who the military believed was in an underground tunnel. That there was huge collateral damage to civilians didn’t seem to be much regretted. It was a particularly aggressive interpretation of the Hannibal Directive that was in due course cancelled or at least clarified – a triumph of which Forensic was part, although as Weizman points out one that is conditional on whatever takes the directive’s place.

Clear-cut victories in this business seem to be rare – it’s still not known, for example, why Temme was in the fatal cafe and why he claimed not to have noticed the shooting. But in the constant struggle to protect truth from becoming a casualty, Forensic’s version of architecture is a powerful weapon.

• Counter Investigations: Forensic Architecture, a selection of Forensic Architecture’s recent and new investigations, will be at the ICA, London, 7 March to 6 May