Even after six months, it’s tough to look at the teddy bear in the glass exhibit case, with a handwritten note penned to its chest.

“Dear Little Boy,” reads the note, which was left at a since-dismantled temporary memorial for eight-year-old Boston Marathon bombing victim Martin Richard. “I am so sorry that you are in heaven. My sister and I just wanted to give you a little gift to show you how sorry we are. From: Isabel and Ava.”

Six months after the bombings and the massive manhunt that ensued, the bear was among a handful of physical mementoes that went on brief display at Northeastern University, where researchers are trying to create a different kind of memorial: not physical, but digital.

“Our Marathon” is a digital archive for which 3,000 photos, videos, oral histories, cyber-updates, and other items have been collected since marathon week. Organizers say the six-month mark is the prime time to collect more.

“We want to try to capture them before people do move on,” says Ryan Cordell, one of the researchers behind the project. “At six months, people can be a bit more reflective, and oral histories become very possible.”