US President Obama says the arrest of the second suspect in the Boston marathon bombings brings to a close one chapter of the tragedy.

19-year old suspect Dzokhar Tsarnaev was found overnight hiding in a back garden but he is said to be badly injured.

His older brother, Tamerlane was killed in a shootout with police yesterday.

Obama said those caught up in the blasts have a right to know what the suspects' motives were, citing the fact that the brothers of Chechen origin are said to have grown up in the United States.

The president said people need an explanation: