A National Guard helicopter prepares to land behind the Watertown Mall as a search for the second of two suspects wanted in the Boston Marathon bombings takes place April 19, 2013 in Watertown, Massachusetts. Thousands of heavily armed police staged an intense manhunt Friday for a Chechen teenager suspected in the Boston marathon bombings with his brother, who was killed in a shootout. Dzhokhar Tsarnaev, 19, defied the massive force after his 26-year-old brother Tamerlan was shot and suffered critical injuries from explosives believed to have been strapped to his body.     AFP PHOTO/Stan HONDA Photo: STAN HONDA, Getty Images / 2013 AFP