By Scott Malone BOSTON (Reuters) - Lawyers for the Boston Marathon bombing suspect sparred with federal prosecutors on Monday over how early in the trial they may discuss his older brother's role in the attack, suggesting the defendant's life may well hang on that question. Dzhokhar Tsarnaev, 21, is charged with killing three people and injuring 264 in the April 15, 2013, attack as well as shooting dead a university police officer as he and Tamerlan Tsarnaev, 26, prepared to flee the city three days later. Tamerlan died that night following a gunbattle with police but defense attorneys described him as the driving force behind the largest mass-casualty attack on U.S. soil since Sept. 11, 2001. "The lead conspirator, the person who started all this and without whom the Boston Marathon bombing would never have occurred, the older brother, is dead ... That presents a problem for the government's request for the death penalty," defense attorney David Bruck told U.S. District Judge George O'Toole.

Georgia halted the planned Monday execution of the only woman on death row in the state due to problems with the drugs to be used in the lethal injection, officials said. Kelly Renee Gissendaner, 46, condemned for the murder of her husband in 1997, would have been the first woman executed by the state in 70 years. "Within the hours leading up to the scheduled execution, the Execution Team performed the necessary checks. At that time, the drugs appeared cloudy," Georgia Department of Corrections spokeswoman Gwendolyn Hogan said in a statement.