A former Malaitan militia commander, Jimmy Rasta, is due to appear in court today charged with murder.
Security forces in Solomon Islands arrested him at Honiara airport, after he arrived from Malaita.
Rasta, also known as Jimmy Lusibea, is alleged to have killed two special constables.
The police commissioner, Bill Morrell, says it took time to collect the evidence to lay the charges.
"It's a matter of collecting evidence, and I think in some cases when people exert a lot of power, they intimidate people, and to get witnesses to come forward can be difficult."
Meanwhile, the Australian foreign minister, Alexander Downer, has welcomed the arrest, describing Rasta as one of the most notorious ex-militants and a man responsible for much of the troubles over the last few years.
Police in Solomon Islands have also arrested a senior officer, Patterson Saeni, on charges of murdering a man in police custody.
