A man remains critically ill in the Royal Victoria Hospital after he was attacked at a barbecue at the weekend.
The scene of the attack in the Waterside area
Police said the attack on 29-year-old Paul McCauley at Chapel Road, Londonderry, on Sunday was sectarian.
They are treating the attack as attempted murder. On Monday night, up to 60 people gathered in the Waterside to pray for Mr McCauley.
They had been invited by Father Aidan Mullan to clear away barricades which had been set on fire by local youths.
Mr McCauley suffered serious head injuries after a gang assaulted him and two other men.
Police said up to eight men were involved in the attack in the Waterside area at about 0340 BST.
One of the other men had his jaw fractured, while a third was badly bruised.
Both were treated in the city's Altnagelvin Hospital and have since been released.
One of the men said he had no idea why they had been attacked.
"We have heard all this talk about sectarianism," he said.
"We had nothing to do with nothing, we were just having a barbecue.
"To pick on my friend like that, if they knew him, they'd know he had nothing to do with anything."
There were disturbances in the area and a hijacking attempt following the attack.
The event was a going away party for a man who was travelling to Azerbaijan to teach.
There were local people and friends who were English, Romanian and Polish, both Catholic and Protestant at the barbecue.
Police said the gang came from the direction of the loyalist Irish Street estate.
Superintendent David Hanna said: "This was a family event in a back garden.
"Upwards of 20 people were there during the day and late evening.
"A number stayed on to help burn rubbish at the back of house in a party atmosphere. This was a purely sectarian attack on innocent people."
Detectives want witnesses to come forward.