Not everyone uses the Apple Health App that’s pre-installed on their iPhones. But this app is playing an important role in a murder trial in Germany. An Afghan refugee named Hussein Khavari is being accused of raping and murdering 19-year-old medical student Maria Ladenburger, disposing of her body in a river.

Hussein has been on trial since September of 2017, and Ladenburger was murdered in October 2016. The authorities wanted to search the information on his iPhone, but Khavari refused to give them his password to unlock the device, Welt reports.. Investigators then turned to a private Munich company to gain access to his phone. Khavari has admitted to his guilt, but he also disputed some details.

Authorities went through the Apple’s Health app on his phone and learned what kind of activity Khavari was participating in on that particular day — the day Ladenburger’s body was dumped in the River Dreisam. They discovered that a large bulk of his activity consisted of “climbing stairs.” They took this information and made a correlation between the time it would have taken Khavari to drag the body of Ladenburger down to the river, and climb back up.

An investigator of similar build to Khavari went to the scene of the crime to recreate how the police believed he disposed of the body. The investigator’s Apple Health app activity correlated with the information that was recorded on Khavari’s phone.

“Digital evidence is already more common in law enforcement, not only metrics from apps but also facial recognition, recordings from smart speakers, and, of course, smart devices with cameras,” said Sean O’Brien, a researcher at Yale Privacy Lab. Michael Kwet, another Yale Privacy Lab researcher, has suggested that data pulled from smartphones and other devices are likely to be used more in criminal investigations. It seems that the legal-system has not yet found a way to handle these kinds of cases.

“In my opinion, the creators and distributors of software should, first and foremost, have a responsibility to their users,” O’Brien said. “When and where they should hand over data to courts is a more complex question. It would be much better, in my view, not to collect such surveillance data at all. Such data is best kept locally on devices whenever possible. If it is collected, those who handle it have a deep responsibility to defend the privacy of their users.”