Accused Boston Marathon bomber Dzhokhar Tsarnaev has pleaded not guilty to committing the worst mass-casualty attack on US soil.
Tsarnaev set off a pair of homemade pressure-cooker bombs along with his brother at the marathon's finish line on 15 April, which killed three and injured about 264.
According to news24, Tsarnaev and his brother, Tamerlan, are also accused of killing a fourth person, a campus police officer, three days later when they prepared to flee Boston.
Tamerlan died in an overnight gun battle with police after killing the officer.
