Forensic radiology is a specialist area in which radiological techniques are used for the purposes  of criminal investigations. Van Rijn's research focuses on the benefits and evidential value of radiological investigations within a criminal investigation. Radiology is playing an increasingly important role in the criminal investigation of violent crime. It offers a non-destructive method of imaging all dimensions of the human body and can therefore add value to the physical examination and/or autopsy. It is a relatively young discipline and uses knowledge of radiology from clinical medicine, although the evidence base for the application of this knowledge in criminal proceedings has not yet fully matured. Van Rijn will be conducting fundamental and applied research and will seek to establish collaborative links with disciplines outside medicine. He will be conducting his research in close collaboration with the Netherlands Forensic Institute (NFI), a link-up that guarantees the forensic relevance of the research.

Van Rijn is one of the founders if the Co van Ledden Hulsebosch Centre (CLHC), an interdisciplinary centre of expertise which brings together eleven research institutes and groups from the AMC, the UvA's Faculty of Science and the NFI. The CLHC was established to combine and support forensic scientific research in Amsterdam. Van Rijn is the forensic radiology coordinator at CLHC.

Van Rijn has been a paediatric radiologist at Emma Kinderziekenhuis, a specialist paediatric centre in Amsterdam, since January 2003. Since January 2010, he has also been working as a forensic radiologist with the NFI in The Hague. Van Rijn is the founder of the Post-mortem and Forensic Radiology Section of the Radiological Society of the Netherlands (NVvR) and the Child Abuse Task Force of the European Society of Paediatric Radiology. He is currently vice-chair of the International Society of Forensic Radiology and Imaging. Van Rijn has authored more than 100 publications in international, peer-reviewed journals, including Radiology, Journal of Forensic Science and Pediatric Radiology.