Forensic Architecture are a multidisciplinary research agency based in London (Goldsmiths University) and Berlin, that use advanced architectural analysis techniques and technology to investigate cases of state violence and violations of human rights across the globe.
In October 2021, Anderson Acoustics was commissioned by Forensic Architecture to undertake a counter-investigation into the audibility of the two gunshots that killed Gabriele Rathjen in Hanau, Germany, on the night of the 19th of February 2020. The killing of Gabriele was but a small piece in the wider impact of the racist attacks that occurred that night.
Forensic Architecture were commissioned by the Initiative 19. Februar, a campaign for Justice for the Victim’s Families, and separately by the lawyer for the Gültekin family, to investigate a series of concerns relating to the investigation.
Investigation Context
On the night of 19th of February 2020, a total of nine (9) people were murdered in the racist attack, which took place in two (2) locations in central Hanau and in the suburb of Kesselsdadt. The victims are:
Said Nesar Hashemi, Sedat Gürbüz, Gökhan Gültekin,
Mercedes Kierpacz, Hamza Kurtović, Vili Viorel Păun,
Fatih Saraçoğlu, Ferhat Unvar and Kaloyan Velkov
1] Local artwork showing the racist attack victims
After the attack, the perpetrator, Tobias Rathjen, fled to his home residence, in the Helmholtzstraße area, where he fired two gunshots, killing his mother (Gabriele Rathjen) in the living room. Sometime after, he fired an additional shot, killing himself.
Tobias and his father, Hans-Gerd Rathjen, were later linked to far-right, white supremacy and conspiracy theory views, that are believed to have provoked the attacks.
[2] Map of the wider Frankfurt area, including the Helmholtzstraße area within Hanau
[3] Helmholtzstraße area in Hanau
Tobias’ father, Hans-Gerd Rathjen, was present in the house when the shots happened. The legitimacy of his testimony has been questioned, in which he claimed to have heard the gunshots to be coming from outside of the house.
Secondly, concerns over the police operation have been raised, where it was claimed that no gunshots were heard in the vicinity where officers were positioned, even though three gunshots occurred before the police entered the property.
The acoustic investigation focused on answering the following questions:
How did the sound of the gunshots spread throughout the surrounding area?
Would it have been possible for police stationed around the house to hear the gunshots?
Was Tobias’ father lying in his testimony?
To bring clarity to these, the assessment would combine 3D modelling with a real-size acoustic re-enactment of the events.
Acoustic modelling
We used innovative techniques to combine external (CadnaA) and internal (CATT-Acoustic) models that replicated both the wider Helmholtzstraße area as well as the conditions inside the house living room at Ground Floor level, as shown in forensic evidence.
[4] External 3D model of the house in the Helmholtzstraße area
[5] Internal 3D model of the Living Room as evidenced in forensic report
[6] Internal gunshot propagation – starting in the living room, reflecting against the surfaces and travelling across the property
Both 3D models provided the foundation to understand how the sound of the gunshots spread from the living room outwards. Firstly, to other parts of the house and then to the outside area.
The results from the modelling showed us what might have happened. However, it was necessary to validate these by taking sound measurements on site. Thankfully, we had access to a nearby house in the area of Hanau, that provided us with the same orientation to the surroundings, as well as identical architectural and structural features to those of the real house.
The only element left to transform in order to mimic the acoustic conditions of the real event, were the actual elements inside the living room.
Life-size Reconstruction
An acoustic model and acoustic treatment advice was provided to the Forensic Architecture team to twin the conditions of the real house, in the experiment house. On-site support to test and refine these was also provided.
[7] Internal 3D model of Living Room as meant to be replicated on site
This process was particularly important, since the amount and distribution of absorptive and reflective surfaces could significantly change the way the sound interacted with the environment as it spread, and it had to be spot on.
[8] Early stage of 3D Computer Model [9] Real-life scale model being built
[10] Forensic Architecture team discussing and refining placement of acoustic elements
[11] Full 3D Computer Model [12] Full scale model in Hanau
Acoustic measurements of a “gunshot”
To avoid alarming nearby residents, the sound of the gunshot, as it was produced by the specific gun and calibre that the perpetrator used, was recreated to provide comparable audio characteristics, without being recognised as such.
[13] Forensic report – Gun and calibre type
[14] Loudspeaker on site [15] Acoustics team with Sound Level Meter
[16] Binaural microphone being used to capture 3D sound
The sound was then played within the life-sized reconstruction of the living room to measure how it spread within the property and in the external areas where the police were positioned.
This included sound insulation testing, which provided valuable insight into how the sound propagated through the ceiling and wall constructions. Testing was also carried out considering multiple possible scenarios of internal and external doors open and closed, as the gaps in evidence suggested that these were possible.
[17] Sound Level Meter recording at nearby position where police were stationed
Gunshot sound propagation
After conducting on-site sound measurements, both internal and external 3D models were calibrated to match the spread of the gunshot.
[18] External gunshot propagation – across Helmholtzstraße area when all doors in the house were opened
Audibility assessment
We measured sound levels and recorded binaural audio at each of the positions in question, to assess the likelihood of audibility. Assessing audibility can be extremely complex and is dependent on the specific hearing ability and mental state of the listener’s themselves.
To remove this uncertainty and to provide a robust argument for the counter-investigation, we assessed the sound of the gunshot in relation to the ambient sound levels during the night in question, which included helicopter flyovers.
[19] Known path of Police helicopter that night
[20] Helmholtzstraße area highlighted in relation to helicopter path
The threshold of audibility was based on the German Standard EN54-23: DIN VDE 0833-2, which aims to demonstrate the likelihood of a Warning Alarm System bringing the attention of a listener to them. The concept being: if the gunshot meets this criteria, then it would be extremely difficult to suggest that the sound was not audible.
Geospatial Audibility Mapping
After using the measurement results to “ground truth” the acoustic model, we predicted likelihood of audibility of the gunshots to the outside areas where police were stationed and to the father’s position in the first floor of the house.
The mapping was provided in GIS format to allow Forensic Architecture to tailor the results in their own unique formatting and presentation style.
[21] Audibility map – Signal-to-noise ratio level of the gunshot against sound level of the helicopter (when helicopter located at 800m height)
Client Testimonial
“Suffice to say that it’s a research project that’s probably a little out of the usual scope of Anderson Acoustics’ work and has asked of your colleagues not only scientific expertise in the field of acoustics but a range of other skills, including investigative lateral thinking, new applications of familiar techniques, on-the-fly problem-solving, and above all a lightness and sensitivity when it comes to engaging with a community of people processing significant trauma, the victims of an appalling racist terror attack.
I’m happy to say that Grant and Ed have excelled themselves in every regard, and have been a valued and crucial part of our team for these recent months. They have been flexible, versatile, and patient in helping us to understand and integrate their expertise, creative in finding solutions, and dedicated and meticulous as we move towards a final report. It has been of immense value to know that they are both available and totally reliable as we try to develop new evidence to support the pursuit of justice and accountability by the people on whose behalf we are working. They are both excellent ambassadors for your company.”
The full film and legacy of the investigation can be found on the Forensic Architecture website.
