TSYRKUNY, Ukraine — To get to the crime scene, the police investigators drove about 30 minutes northeast of downtown Kharkiv — past neighborhoods in ruins, destroyed Russian military vehicles, a field littered with blast craters, and plumes of dark smoke rising a few miles in the distance, where fighting between the Ukrainian and Russian militaries was ongoing.

The Ukrainians had expelled Russian forces from the town of Tsyrkuny, less than 20 miles from the Russian border, just three days earlier — part of a Ukrainian counteroffensive that has reclaimed a significant swath of territory in the Kharkiv region this month.

Now the police investigators were eager to visit the village, where they had a report of two civilian bodies lying on the side of a dirt road. The women had been killed by a Russian land mine weeks earlier, the police said. And just as forensic scientists would visit the site of a killing in prewar times to collect evidence, they needed to do the same here in their quest to gather evidence of potential Russian war crimes — a process taking place across the country that led to the announcement of a first prosecution on Wednesday, a 21-year-old Russian soldier who is in custody.