PARIS—In normally quiet Copenhagen on Saturday afternoon, a gunman opened up on a café where Swedish cartoonist Lars Vilks was to talk about why he drew the head of the Prophet Muhammad on the body of a dog back in 2007—and why he’d had to have armed guards since. Dozens of bullets blasted through the café windows, killing a documentary filmmaker and injuring others before the attacker or attackers, at first believed to be two men, made an escape along narrow Sankt Peders Straede.

A friend wrote to me from near the scene shortly afterward that the streets of Copenhagen were empty, and "the only sounds are the police sirens."

With the Danish capital on virtual lockdown, the killing continued, and the next target—in what is becoming a predictable pattern in Europe's new age of terror—appears to have been a synagogue. It was the city's most important, in Krystalgade, less than a ten minute walk from the scene of the first shooting. A security guard at the synagogue was killed nearby with a gunshot to the head and two police officers were wounded before the shooter fled once again.

Late Saturday evening, Morten Frich, a journalist and news editor at Berlingske, one of Denmark's national newspapers, signed off for the night with the day's grim tally.