Boston bombing suspect indicted on criminal charges A federal grand jury on Thursday indicted the accused Boston marathon bomber Dzhokhar Tsarnaev on charges of killing four people in the largest mass-casualty attack on US soil since September 11, 2001. The 30-count indictment filed in Boston federal court charges the 19-year-old ethnic Chechen with setting off two homemade pressure-cooker bombs in a crowd of thousands at the race's finish line and with committing a carjacking and engaging in a fierce gun battle with police before his April 19 arrest. Mr Tsarnaev faces the possibility of execution if convicted. His public defender, Miriam Conrad, declined to comment on the charges, which cover a four-day period that traumatised the Boston area. The April 15 bombing was followed by the shooting of a campus police officer in Cambridge, a carjacking and a late-night gun battle with police in the nearby suburb of Watertown. Dzhokhar's 26-year-old brother Tamerlan died in the gun battle, which led to a daylong lockdown of most of the metropolitan area. That evening, Dzhokhar was found hiding in a boat in a resident's backyard and arrested after police fired a hail of bullets. The brothers started preparing for the attack more than two months earlier, when Tamerlan travelled to a New Hampshire fireworks store to buy 48 mortar shells containing about 3.6kg of explosive powder, according to the charges. Three people died in the bomb attacks: 29-year-old restaurant manager Krystle Campbell, 23-year-old graduate student Lingzi Lu and 8-year-old Martin Richard. A campus policeman was also killed in their attempt to escape arrest. Tamerlan Tsarnaev had been on a US government database of potential terrorism suspects and the US had twice been warned by Russia that he might be an Islamic militant, according to US security officials. A congressional hearing after the bombing focused on whether the Federal Bureau of Investigation paid sufficient heed to Moscow, which has been in bitter conflict with Islamic militants in Chechnya and other parts of the volatile northern Caucasus region. The Tsarnaev brothers" ethnic homeland of Chechnya, a mainly Muslim province that saw centuries of war and repression, no longer threatens to secede from Russia. But it has become a breeding ground for a form of militant Islam whose adherents have spread violence to other parts of Russia, and may have inspired the radicalisation of the Boston bombers. The indictment follows the pair through the day of the bombing and to the evening of April 18, after the FBI released pictures of both men at the finish line, in a plea for help from the public in identifying them. The pair armed themselves with five more homemade bombs, a semi-automatic handgun, a machete and a hunting knife. They then drove to the Massachusetts Institute of Technology in Cambridge, where they shot their fourth victim. Campus police officer Sean Collier died during their unsuccessful attempt to steal his weapon. The indictment details how the two carjacked a Mercedes, briefly holding its driver hostage. They drove to Watertown, where police found them shortly after midnight. The gun battle followed, with the brothers shooting and throwing bombs at the police. Dzhokhar, who had left the car during the battle, jumped back into the Mercedes and drove at the police officers who had been trying to arrest them. In the confusion, he ran over his brother, contributing to his death. That move allowed Dzhokhar to escape and prompted a day-long lockdown of most of the Boston area. That evening, a resident found him hiding in a boat in a Watertown backyard, on which he had written messages including: "The US government is killing our innocent civilians" and "I can't stand to see such evil go unpunished," the indictment reads. The younger Tsarnaev, who was badly injured in that gun battle, has been held in a prison hospital west of Boston since his capture on April 19.