Facebook has a long-maligned yet still active feature called “People You May Know.” It scours the network’s data troves, picks out the profiles of likely acquaintances, and suggests that you “friend” them. But not everyone you know is a friend.

Anthropologist Dragana Kaurin told me this week about a strange encounter she had with it some years back.

“I opened Facebook and I saw a face and a name I recognized. It was my first grade teacher,” she told me. Kaurin is Bosnian and fled Sarajevo as a child, at the start of the war and genocide that took hundreds of thousands of lives between 1992 and 1995. One of Kaurin’s last memories of school life in Sarajevo was of that very same teacher separating children in the classroom on the basis of their ethnicity, as if to foreshadow the ethnic cleansing campaign that soon followed.

“It was widely rumored that our teacher took up arms and shot at civilians, and secondly, that she had died during the war,” she said. “So it was like seeing a ghost.” Now at retirement age, the teacher’s profile showed her membership in a number of ethno-nationalist groups on Facebook.