"He has then been shot twice before the offenders cowardly ran from the scene," Detective Inspector Tofilau Faa Va'aelua said.
"This is a senseless act of violence that has left a newborn baby to grow up without a father. Mr Brown was unarmed, out-numbered and defenceless."
Brown is survived by his wife Atiliai Brown, who recently gave birth, while the couple had only been married for less than two months.
Va'aelua said police executed several search warrants yesterdaywith the assistance of the Armed Offenders Squad, leading to the accused's arrest.
Several firearms were also recovered during the morning raids, Va'aelua said.
Two other people were also assisting police with their inquiries, he added.
Va'aelua said many police officers have worked on the homicide inquiry since Brown's death.
"[Yesterday's] arrest is pleasing and a great relief to achieve this result," the detective said.
"This has come about through some tireless work by the police team working on the case and assisted by information provided from the public, including anonymous reports via Crimestoppers."
The funeral for Brown, who was also known as Afa, was also held yesterday.