This week, a Connecticut jury convicted Richard Dabate of murder in the killing of his wife, Connie Dabate, after a five-week-long trial that hinged — in part — on data from her Fitbit. Richard said a man dressed in camouflage broke into their home in 2015 and shot Connie. But Connie wore a Fitbit, and data from the device showed movement for around an hour after Richard said the break-in happened.

To make the case that the Fitbit data helped show Richard killed Connie, prosecutors called on Keith Diaz, an exercise physiologist and professor at Columbia University Medical Center. Diaz has done studies validating the accuracy of Fitbits and testified about their precision.

Diaz often testifies as an expert witness in criminal trials. He told The Verge that it’s personally gratifying to participate in trials but that it’s also a challenge. The way he usually thinks about Fitbit data as a scientist is different from the way he’s asked about it in a courtroom. “The scientific questions we’re answering are different from the criminal questions,” he says. “What I’ve strived to do in these cases is translate that.”

Fitbits are generally accurate devices, Diaz says, but they’re by no means perfect. For scientific research, that’s expected — nothing is ever absolute, and it’s rare to get an answer that comes with 100 percent certainty. Science lives with some amount of statistical error. But the law operates under different guidelines: it wants to know if something happened beyond a reasonable doubt. “This has very serious implications for if someone could go away for 25 years to life,” he says. “So is it okay to live with some gray area — and under what conditions? That’s been some of the challenge and the hurdles