Police have increased their patrols to tackle the "community tension" in an area of Manchester after a teenager was stabbed to death.
John Muldowney, 18, was found unconscious in a house on Hollyhedge Road in Benchill, shortly after 0300 GMT on Monday.
He had been stabbed in the chest and was pronounced dead a short time later.
A fourth person has been arrested in connection with the killing, Greater Manchester Police said.
The 26-year-old man is being held on suspicion of murder.
Another man, 23, who was arrested on suspicion of murder on Monday remains in custody.
A 24-year-old woman, arrested on suspicion of murder, and a 41-year-old woman, held on suspicion of assisting an offender, have both been released on police bail.
Supt Hughie Hardiman said: "We understand that the community has been left deeply shocked and saddened by the news of John's death.
"This has led to some tension in the community. I appreciate this is a difficult time but we ask for residents to remain calm whilst we complete a thorough investigation.
"We have stepped up patrols in Benchill so that should anyone have any concerns, they can speak to the patrolling officers.
"We are there to provide reassurance to residents, address their concerns and prevent any further crime or disorder.
"We are also keen to hear from anyone who has information about the events that led to John's death."