Police were last night questioning a close friend of murder victim Robert McCartney in connection with the shooting of former IRA commander Gerard 'Jock' Davison.
Brendan Devine was arrested in north Belfast yesterday.
A property was also searched in relation to the murder of the 47-year-old community worker, who was gunned down in a residential street in the Markets area of the city on Tuesday morning.
Devine suffered injures, including having his throat cut with a broken bottle, when a fight broke out in nearby Magennis's Bar in 2005.
The fight spilled out onto the street where Mr McCartney was fatally stabbed.
The 41-year-old was later a key prosecution witness in the trial of three men accused of involvement in the murder.
All three, including Jock Davison's uncle Terence Davison, were later acquitted of all charges.
The murder of the former member of the IRA's 'northern command' has caused shock among republicans.
His funeral, which is expected to take place with full republican honours, may be postponed until Monday following a delay in the body being returned to the family.
The father-of-three was shot several times in the head and chest as he walked to work at around 9am on Tuesday.
A close relative of a man murdered by the IRA in the early 1990s is believed to be the chief suspect in the murder.
Parish priest Fr Michael McGinnity yesterday urged anyone with information to contact police, describing the murder as a "depraved and diabolical crime".
The group Republican Network for Unity also spoke yesterday of its "shock and sadness" at the murder.
Hours after Mr Davison’s killing police said they didn’t believe dissident republicans had been involved in the shooting.
