The second suspect in the Woolwich murder was known for handing out radical leaflets, and a woman believed to be his girlfriend had recently converted to Islam.
Other details known about the man, said to be Michael Adebowale, are that he is 22 and that he frequented the area of southeast London where Thursday's atrocity took place.
He is in hospital after being shot by armed response officers but his injuries are not life-threatening, a Scotland Yard spokesman said.
The man is six years younger than his fellow suspect and in video clips captured by passers-by his behaviour seemed less volatile.
He had been seen frequently by neighbours at a block of flats in nearby Greenwich, which was raided by armed police yesterday.