Boston Marathon Bombing

Obama Attends Services for Boston Victims

Authorities still working to identify people in video

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President Barack Obama on Thursday attended an interfaith service in Boston for the victims of the Boston Marathon explosions as federal investigators said they were working to identify a person in a video who appeared to leave a bag in the spot where one of two bombs later exploded.

Authorities also were trying to identify at least one other person seen in videos of the crowd, according to people familiar with the matter.