To borrow a line from Dennis Green, they are who we thought they were. From his hospital bed, Dzhokhar Tsarnaev has acknowledged his role in planting the explosives near the marathon finish line on April 15, the officials said. The first successful large-scale bombing in the post-Sept. 11, 2001, era, the Boston attack killed three people and wounded more than 250 others.The officials, who spoke on condition of anonymity to describe an ongoing investigation, said Dzhokhar and his older brother, Tamerlan Tsarnaev, who was killed by police as the two attempted to avoid capture, do not appear to have been...