Two children remain in critical condition at the hospital with serious leg injuries. Mooney said that tourniquets applied by emergency responders at the race saved the children's lives.
Doctors at Massachusetts General Hospital also say they removed metal fragments from victims of the two bombs.
Dr. Stephen Epstein of the emergency medicine department at Beth Israel Deaconess Medical Center said he saw an X-ray of one victim's leg that had "what appears to be small, uniform, round objects throughout it — similar in the appearance to BBs."
Massachusetts General treated 31 victims of the bombs. The hospital performed four amputations and at least two more patients have legs that are still at risk of amputation, Dr. George Velmahos said.
AP writers Eileen Sullivan in Washington and Mark Pratt in Boston contributed to this report.