The Boston Globe has signed a deal with Dutton to write the definitive account of the Boston Marathon bombings. Brian Tart, president and publisher of Dutton, said the book, to be written by Globe reporters Scott Helman and Jenna Russell with the aid of the newspaper’s team of investigative reporters and editors, will tell the story of the bombings, the manhunt that followed, and the city of Boston’s efforts to overcome the devastating effects of the attack. The book, to be published in time for the first anniversary of the tragedy, will weave a narrative chronicling the story of that day and those who were affected — the runners, the victims, the doctors and first responders, the perpetrators — and the heroic deeds of ordinary citizens. The book, still untitled, is expected to provide an unprecedented level of detail and insight, including behind-the-scenes glimpses of the police and FBI as they puzzled over questions related to the case, such as whether to release photos of the Tsarnaev brothers. The book promises to be a portrait of a city on its worst day; but also at its best.