A 51-year-old man is on a life support machine after being attacked in west Belfast.
Former republican prisoner Frank McGreevy was assaulted at his home in Ross Street shortly after 1830 GMT on Saturday.
Police are treating the incident as attempted murder. A 20-year-old man is being questioned by police.
Acting Detective Superintendent Jeff Smyth said they were following a definite line of inquiry.
"As such last evening in the middle of the night, members of the PSNI, under my direction, searched a number of houses in this community looking for a suspect," he said.
The Chairman of the Falls Road Residents' Association, Robert McClenaghan, knows the victim well.
He said: "He is a former prisoner who served a life sentence. So he would be very well known.
"For something as brutal as this to happen to him, is a real shock to all of us in the community who knew him over many, many years."
Detectives later said the 20-year-old man had handed himself in at Grosevnor Road police station.
Any witnesses to the incident have been urged to come forward.
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