Two men, aged 21 and 33, are in custody being questioned on suspicion of murder after two teenagers were shot in Milton Keynes on Thursday night.
A 13-year-old boy has been released on police bail pending further inquiries.
Mohamed Abdi Farah, 19, of Birmingham, died in Fishermead Boulevard and Amin Ahmed Ismail, 18, of London, later in hospital. Both were shot in the head.
Police said three males from Bletchley had been arrested on Friday. The victims were originally from Somalia.
Somali community leaders in Milton Keynes are helping Thames Valley police with their inquiries.
Leaflets appealing for help and information have been published in English and Somali and are being distributed across the town.
Det Supt Rob Mason, leading the investigation for Thames Valley Police, said: "Although we have made a number of arrests, I am keen to stress that we are still in the very early stages of the investigation.
"I would continue to urge anyone with information about the incident to contact police urgently."
Police said both Mr Farah and Mr Ismail, who had been in Milton Keynes for some time, were known to them for minor offences.
Detectives have ruled out the killings being gang-related at this stage.
Mr Mason said: "A large area of Fishermead is currently sealed off while officers carry out investigations and protect the scene.
"I appreciate that residents will feel concerned about this incident. However, there is a large and highly visible police presence in the area.
"I also appreciate that there will be a lot of rumour and intrigue in the community.
"However, we are at the very early stages of this investigation and as such cannot speculate on possible reasons for the attack."
He added: "We believe that the victims in this incident are friends, but we do not know if the offender is known to them."
Thames Valley Police has released two videos on YouTube to appeal for witnesses, one in Somali and one in English.
Crimestoppers is offering a reward of up to £5,000 for information leading to the arrest and conviction of those responsible for the shooting.