Warrants were issued after the murder for the alleged gunman, Suchat Nimlaor, and his supposed driver, Eakachai Nimlaor, after the arrest of four others said to have been involved in the murder, including Denis Cavatassi, also Italian, a business partner of Mr Butti.
Copies of the warrants have been sent to police in other provinces, especially in the south of Thailand where police believe the two suspects are hiding.
Mr Butti was allegedly followed by Suchat and Eakachai who assassinated him close to the entrance to the Bang Pae waterfall in Tambon Pa Khlok.
Cavatassi allegedly hired Prasong Yongkit, who was arrested along with him, to arrange the murder team to kill Mr Butti.
Police believe the murder was motivated by B9 million that Mr Butti had supposedly embezzled from the business the two owned. Cavatassi, however, has insisted on his innocence.
Initially Cavatassi was denied bail because the court considered him a flight risk. On July 22, however, he was released on bail. Police are tight-lipped about the amount paid for his surety, but The Phuket News understands that it was well over a million baht.
His trial is expected to begin sometime next year.