Police in the German state of Bavaria will have new powers to use forensic DNA profiling after a controversial law passed today in the Landtag , the state parliament in Munich. The law is the first in Germany that allows authorities to use DNA to help determine the physical characteristics, such as eye color, of an unknown culprit.

The new DNA rules are part of a broader law which has drawn criticism of the wide surveillance powers it gives the state’s police to investigate people they deem an “imminent danger,” people who haven’t necessarily committed any crimes but might be planning to do so.

Today’s move was prompted, in part, by the rape and murder of a medical student in Freiburg, Germany, in late 2016. An asylum seeker, originally from Afghanistan, was convicted of the murder and sentenced to life in prison. But some authorities complained that they could have narrowed their search more quickly if they had been able to use trace DNA to predict what the suspect would look like. Existing federal and state laws allow investigators to use DNA only to look for an exact match between crime scene evidence and a potential culprit, either in a database of known criminals or from a suspect.

In 2017, federal authorities proposed allowing investigators to conduct broader DNA profiling, but the proposal stalled after critics called for an expanded ethical debate on the advantages and disadvantages of the techniques. One critic, Veronika Lipphardt, a professor of technology studies at the University College Freiburg, noted that the crucial evidence in the Freiburg murder case was something no DNA analysis could provide: a strand of hair that had an usual dye pattern—dark at the root, blond at the ends. Police used surveillance video from a tram stop near the crime scene to find a suspect with the same dye pattern.

In Bavaria, the governing Christian Social Union decided to move forward with expanding investigative uses of DNA. Specifically, the new law will allow law enforcement officials to analyze trace DNA samples for genetic markers that help determine hair color, eye color, skin color, age, and “biogeographical ancestry.”

Some analysts worry expanded DNA use could have problematic outcomes. For example, Lipphardt and others caution that although the science behind forensic DNA profiling is solid, it still comes with significant uncertainties that can be easily misunderstood by police and the public. “The proponents are framing this as the most safe, secure and objective technique available. But they exaggerate the numerical certainties,” she says. “That creates the impression that it’s clear-cut what race someone is or where someone comes from, and that’s not true.”

“You would need a lot of training of police forces to use it responsibly,” says Carsten Momsen, a professor of law at the Free University of Berlin, who worries the technique could lead to inaccurate profiling and targeting of minority groups.

But Manfred Kayser, a geneticist at Erasmus University Medical Center in Rotterdam, the Netherlands, who has worked to develop several of the techniques permitted under the new law, says they have been used successfully in France, the Netherlands, and the United Kingdom. “There has to be education and training involved,” he says. “You have to be able to work with probabilities.” But he says police are constantly evaluating different kinds of evidence and assessing its credibility. “If there’s a 95% chance of blue eyes, then you can evaluate that accordingly.” If a probability is lower—which is common for such eye colors as green, brown, or hazel—then the investigators are at least aware of that uncertainty, he says. In contrast, he notes, “with eyewitness testimony you have no idea if it’s right or wrong.”

Other aspects of the law are drawing fierce opposition. An estimated 30,000 people turned out in Munich last week to protest the measure—one of the largest demonstrations in the city in the recent years. State leaders have said the new surveillance powers are necessary to thwart potential mass shootings, terror attacks, and violence by stalkers. However, opposition parties and other groups say the new law goes too far in allowing police to intercept mail, hack into electronic communications, and even use drones to track people they deem suspicious. Previously authorities had to demonstrate that a person posed a “concrete threat” before they could take such steps.

Opponents of the law have said they will challenge the new measures in court. If the law withstands those challenges, observers say, other states and the federal government are likely to adopt similar measures.