`` These two acted together and alone , '' he said . Dzhokhar Tsarnaev was seen on campus , at night after marathon bombings . Younger brother was seen hiding in boat after manhunt . Police sought him after analyzing photos from scene . Older brother died in hospital , was run over by Tsarnaev , witnesses say .
Dzhokhar Tsarnaev was seen on campus , at night after marathon bombings . Younger brother was seen hiding in boat after manhunt . Police sought him after analyzing photos from scene . Older brother died in hospital , was run over by Tsarnaev , witnesses say .