Detectives investigating the shooting of a 17-year-old boy are continuing to question two teenagers.
Lewis O'Brien was shot inside a house in Huyton, Merseyside, on Wednesday afternoon.
The youngster, who neighbours said was nicknamed "OB", was pronounced dead on arrival at hospital.
A post-mortem examination revealed he died of a single gunshot wound to the chest.
An 18-year-old man arrested on Wednesday night has been bailed pending further inquiries, Merseyside Police said. Two youths, aged 15 and 17, remain in custody, where they are being questioned on suspicion of murder.
A 39-year-old woman, who was arrested on suspicion of assisting an offender, was released without charge and will face no further action, police said.
Officers were called to the house, on Hathersage Road, shortly before 4pm on Wednesday.
Det Ch Insp Richard Carr said detectives are still trying to piece together what happened in the lead-up to the shooting. "I would like to appeal to anyone with any information about the incident or events leading up to it to come forward," he said.
"This incident has resulted in a young man's life being needlessly cut short. There is no place for guns on the streets of Merseyside and with the help of, and information from, the community we will relentlessly pursue this investigation."
Mr Carr said police patrols in the area have been stepped up to reassure residents. The house where the shooting took place remained sealed off and only residents were allowed in and out of the immediate scene.
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