“Mmm.”

“But we don’t.”

“There’s something about these places,” said Ringmar. “It’s not just coincidence.” Then he added as if talking to himself: “It rarely is.”

Halders made no comment, but he knew what Ringmar meant. The location of a violent assault was often significant. The attacker, or the victim, nearly always had some kind of link with that particular spot, even if it wasn’t obvious from the start. The location is always key. Always start off with the location. Spread your search out from there.

“I’ve had a word with Birgersson,” said Ringmar. “After the Guldheden incident. We’re probably going to get a few more officers so that we can knock on a few more doors.”

Halders could see the superintendent in his mind’s eye. As scraggy as the vegetation in the far north where he grew up, chain-smoking after yet another failed attempt to quit.

“What about the triangle?” asked Halders. “The triangle theory? Add the third line and you’ve got a right triangle.” Halders ran his finger over the map from Doktor Fries Square to Linnéplatsen.

“No. You’re the first to come up with that fascinating link.”

“Cut the sarcasm, Bertil. You’re too nice a guy for that kind of thing.” Halders grinned. “But Birgersson has a soft spot when it comes to math, I know that, especially geometrical shapes.”

Halders grinned again. Maybe it was Sture Birgersson who did it. Nobody could fathom the man. Once a year he would disappear, nobody knew where. Winter maybe, but maybe not. Maybe Sture was wandering around the streets in a black cloak, wielding the mechanical cloudberry picker he’d had as a kid and using it to draw crosses on students’ heads. Halders could picture his silhouette in the light from the street lamp: Doctor Sture. Afterward, Mister Birgersson. One might ask which of them was worse.

“So you think we’d get more officers because we can see a geometrical shape here?” wondered Ringmar.