A 20-year-old man was being questioned in connection with the murder of man who was repeatedly knifed on a London bus.
Richard Whelan, whose family is from Donegal, was stabbed several times on the top deck of a No43 bus as he made his way home from a night out with his girlfriend in north London
The 28-year-old was taken to the nearby Whittington Hospital, where he died.
The man was arrested at an address in Walton-on-Thames, Surrey, last night and taken to a London police station where he remains in custody.
A Met spokeswoman said they were still trying to trace a number of potential witnesses known to have been aboard the bus on the night of the stabbing.
Mr Whelan was was stabbed as he returned home from a night out in Upper Street, north London, when he asked a hooded youth to stop throwing chips at his girlfriend.
Police said Mr Whelan, a hospitality agent of Kentish Town, north London, was stabbed stabbed around six times in a "totally unprovoked" attack on July 29th.
Just weeks earlier he had led the hunt for Irish man Ciaran Cassidy (22), until it was confirmed that his close friend had been a victim of the July 7th bombings.