He was stabbed at the Rincon Costeno Restaurant in Hampton Street where he worked in the family business.
The suspect, who was stopped by British Transport Police for allegedly evading his fare at Edmonton Green station in north London, has been released on bail pending further investigation.
A Met police statement said: “On Friday, 10 June a 20-year-old man was arrested on suspicion of murder of Ian Gualavisi in Elephant and Castle. The man has been bailed pending further enquiries.
“He was originally detained by officers from British Transport Police.
“Six other people have been arrested as part of this investigation.”
Two men, both aged 24, arrested on 15 and 16 December 2021 on suspicion of murder, have been released under investigation.
“Four males, aged between 16 and 21, were arrested on 25 and 26 May 2022. They have been bailed to return pending further enquiries”, police said.
Mr Gualaviso was an ambitious young man who wanted to open other Ecuadorean restaurants across London, his family said at the time of his death.
The murder was featured on BBC’s Crimewatch Live programme.
Police described him as “a young man embarking on a new phase of his life”. He died in front of his parents.
A BTP spokesperson said: “British Transport Police responded to a report of a fare evader at Edmonton Green railway station at 5.31pm on 10 June.
“Officers engaged with the 20-year-old man and identity checks revealed he was wanted by the Metropolitan Police Service in connection to a murder. He was arrested on suspicion of conspiracy to murder and conveyed to police custody.”
Superintendent Mark Lawrie was one of the officers involved in the arrest.
He tweeted: “On patrol in north London @BTPOSU went to assist rail staff who were dealing with a young man who hadn’t paid his fare... After some extensive checks to confirm his actual identity, found he was wanted for Murder and was deposited to the grateful detectives at Lewisham MetPol.”
On patrol in north London @BTPOSU went to assist rail staff who were dealing with a young man who hadn't paid his fare... After some extensive checks to confirm his actual identity, found he was wanted for Murder and was deposited to the grateful detectives at Lewisham MetPol 💪
— Supt Mark Lawrie (@BTPLawrie) June 13, 2022