The directors of the HBO documentary about the Boston Marathon bombings have done plenty of their own research and reporting, but they’re looking for something else. Ricki Stern and Annie Sundberg, the directing duo behind the still-untitled HBO doc, are soliciting short videotaped statements from runners, first responders, survivors, and others who may have been affected by the events of April 15, 2013. “These would be people’s personal stories that we could use in a montage, to step back from the intimate stories we’re telling,’’ said Stern. The filmmakers have created a website — www.bostonprojectdocumentary.com — where people can add videos. The filmmakers point out that Break Thru Films will have non-exclusive right and license to use and include the submitted material in any and all versions of the documentary. (The Globe is a partner with Break Thru Films/HBO on the project.) Stern and Sundberg, whose films include “Joan Rivers — A Piece of Work’’ and “Knuckleball!,’’ about pitchers Tim Wakefield and R.A. Dickey, have been working on the film since last summer. It likely would not air until 2017.