On a blustery Sunday in May, The New York Times' Deborah Acosta bent down and picked up a piece of a mystery on a New York City sidewalk. Acosta had recently been reassigned to Times' Facebook Live team. Her new focus: the city.

"So I think my eyes were especially peeled that weekend," Acosta said.

When she came across Kodachrome slides strewn across the sidewalk, she immediately started filming herself picking them up. Maybe this could be a cool side project, she thought. And then — maybe this could be a cool Facebook Live broadcast. Acosta emailed her editor, Louise Story, a little of the video she'd shot.

The rest of what happened that day — and the sleuthing that ensued — can be found in "Fragments of a Life: A Curbside Mystery." The 10-minute video tells the story of how the vivid slides ended up on the sidewalk and how they eventually led back to another journalist — Mariana Gosnell, who died in 2012.

This curbside mystery began just as the the Times' Facebook Live team was beginning to come up with storytelling ideas. One category that's developed since Acosta picked up that first slide: live interactive reporting.

"Doing really effective live interactive journalism is quick and it is somewhat open to chance," said Story, "but good planning does make a difference."

Acosta first went live with the slides on May 15. Three days later, she and Times' photographer Todd Heisler went live to talk about the images in the slides.

The slides and the story were put on hold for awhile as Acosta pulled back to cover big news elsewhere. When it came time to answer the questions the discarded slides presented, the person who could answer them was hesitant to go live, Story said.

So, they brought him into the studio. That footage inspired the team to piece together the story's many parts into a single video. The Times brought its Facebook live audience into the video to narrate their comments and gave them a mention in the credits.

"Stylistically, this really has its own feel," Story said, "in part because we were trying to keep the tone of live in this throughout."

In evaluating the resulting audience engagement, the Times isn't just looking at the number of people that tuned in live (they peaked at more than 6,300 in the first livestream). They also examine how the audience reacts to the videos in the days and weeks since they initially streamed.

Every installment of the project had significant viewership, Story said, and heavy sharing, "so this is something that, after the initial push of The New York Times, the wings of our audience are carrying this forward."

This isn't the Times' only Facebook Live project. They're solving crossword puzzles together and bringing their audience along for reporting trips. Their livestreaming projects, including "30 Under 30" and "Whistleblowers," aren't linked back to articles, and more than 150 Times journalists have participated, some multiple times, in live interactive journalism.

The projects are successful, she said, because the journalists are genuinely passionate about the subject matter. She remembered something Acosta said when she first discovered the slides of a journalist who died four years earlier.

"She said, 'these are beautiful, no one who made this kind of work would want it thrown away.'"

Now, in a way that didn't exist in Gosnell's lifetime, it won't be.