All day Sunday, police directed traffic around a blocked-off section of Boylston Street in downtown Boston where bombs had gone off nearly a week earlier, killing three and wounding hundreds. A makeshift memorial had been set up to honor the dead with personal messages and flowers, and old running shoes hung from metal barricades. Similar makeshift memorials were set up in suburbs outside the city proper, at least one designed in the dried blood of a dead suspect.

About a mile northwest from Boston’s ground zero, across the Charles River in Cambridge, a small but notable memorial had been set up. This one lay on the Massachusetts Institute of Technology’s campus, on a concrete walkway beside MIT’s Ray and Maria Stata Center. Famous for its Frank Gehry-designed architecture, Stata is all kitty-cornered frames and weirdly metallic boxes, like something out of a futuristic claymation video or Pee-wee’s Playhouse. This memorial seemed out of place. It was set up to honor an MIT police officer, Sean Collier, who had been shot and killed here while on duty, allegedly by the brothers suspected of carrying out the bombings downtown days earlier.