Police officers secure a school building at the Massachusetts Institute of Technology near where a police officer was shot in Cambridge, Massachusetts April 18, 2013.KRISTYN ULANDAY/Reuters
What is the most recent news?
Authorities say one of the two suspects in the Boston Marathon bombings has been killed after a violent gun and explosives battle with police. The second suspect escaped and is the subject of an intense manhunt.
They have identified the dead man as Tamerlan Tsarnaev, 26, and say they are looking for his brother, Dzhokhar A. Tsarnaev, 19.
A Massachusetts Institute of Technology police officer was killed earlier in an apparent encounter with the two suspects.
All Boston residents have been told to stay in their homes as the intense search continues for the second suspect, who is described as extremely dangerous and a terrorist.
Who are the suspects in the bombing?
The two brothers suspected to be the bombers are originally from Dagestan, a turbulent area of Russia near Chechnya.
The brothers had been living in Cambridge, just outside Boston. Dzhokhar lived in Turkey before moving to Massachusetts where he was studying at the Cambridge Rindge & Latin School. In 2011, he received a scholarship from the school.
The brothers' parents live in Russia.
Three unanswered questions
1. What was the motive? There's little evidence to this point about why the suspects decided to stage an attack. The fact the brothers have been identified as Chechen has led to a lot of speculation but there's nothing in their public writings to suggest a commitment to or training for terrorism. And why target a sporting event, the Boston Marathon, rather than a more symbolic American target?
2. How did the second suspect escape? Officials say the suspects engaged in a gun and explosives battle with police. One was killed but the other got away. How is that possible with so many officers on the scene? Why has there been no concrete public information on his whereabouts?
3. Were others involved? Some reports suggest officials are looking for accomplices. But no evidence has been released that anyone other than the two suspects participated in the bombings. It's unclear why authorities believe someone or some group are helping the second suspect escape.
What happened at the marathon
At least three people are dead and more than 170 wounded after two bombs exploded Monday afternoon.
The first bomb, located near the finish line of the 26.2-mile course, exploded at 2:50 p.m., at 4:09:44 into the 117th Boston Marathon. This was just minutes before the average finishing time of the 2012 race. A mere 10 seconds later – and only 100 yards away – a second explosion happened. This one was located along the 26th – and final – mile, which was dedicated to the 26 lives lost in the Newton school massacre.
The bombs were crudely built, fashioned out of pressure cookers filled with explosives. One of the cookers contained pieces of metal and ball-bearings, and the other with nails. Both bombs were placed inside of nylon bags, officials said.
Who was hurt?
At least 176 people were injured, 17 critically. Martin Richard, an eight-year-old boy from Dorchester was among the three deceased. Krystle Campbell, a 29-year-old restaurant manager who had gone with a friend to watch the race, was another. The third victim was identified as Lu Lingzi, a student doing graduate work at Boston University.
Thursday morning, U.S. President Barack Obama and First Lady Michelle Obama attended an inter-faith ceremony in honour of the Boston victims.
Were any Canadians hurt?
The marathon attracted more than 23,000 participants, 2,078 of them from Canada. There were no reports of any Canadians being affected by the blasts, according to the Department of Foreign Affairs.
With reports from The Associated Press and Globe staff
Ann Hui