The Boston bombing suspect remains in hospital under heavy guard.

19-year-old Dzhokhar Tsarnaev is said to be in a stable condition after suffering gunshot wounds in a shootout with police in which his older brother Tamerlan died.

Police in Massachusetts say they believe the two brothers acted alone but have yet to uncover a motive.

Information is gradually emerging about their personal lives and what role their Chechen heritage may have played.

Dr Peter Neumann is from the International Centre for the Study of Radicalisation. He believes they carried out their research online: