Mr McMenamin was attacked in Rosemount Avenue

A 20-year-old man remains critically ill after the assault on Sunday.

A husband and wife are under arrest in connection with the incident.

Don McMenamin was taken to Altnagelvin hospital with serious head injuries after he was attacked in Rosemount Avenue at about 0400 BST.

Three men and a woman who were arrested in connection with the incident were released on Monday.

A man in his 30s was released on police bail, pending further inquiries.

We are just a family dealing with a young man of 20 years of age, lying in hospital in a serious condition Charlie McMenamin Victim's uncle

Two men and a woman were freed without charge.

Friends of Mr McMenamin said he had just returned to Derry from a night out in Letterkenny in County Donegal.

Detective Chief Inspector Tom Woods said the victim was attacked after helping to stop a fight.

He said the dispute appeared to have been settled when a man got out of a dark coloured car and approached the group.

"He then returned to the car and returned with what we believe was a silver heavy object which he used to strike one of the group on the head.

"This caused serious injury to the party involved and as a result that young man is currently in Altnagelvin Hospital fighting for his life.

"It appears to be a pointless motiveless attack and it has left a family shattered."

'A good heart'

Detectives said they want more public help with their investigation.

They said it was vital that anyone with information should come forward.

They want people who were in the area around the time of the assault to contact them.

The victim's uncle, Charlie McMenamin, said the family was in shock.

"We are just a family dealing with a young man of 20 years of age, lying in hospital in a serious condition.

"He has a good heart - we are just holding out hope that he will pull through it."