The arrests came after the police found the dismembered body of Hans Peter Ralter Mack inside a freezer at a residence in Chokchai Garden Home 1 Village in the early hours of Tuesday morning.
They are Germans Petra Christl Grundgrief and Olaf Thorsten Brinkmann and Zahrouk Kareen Uddin, a Pakistani with Thai nationality.
Grundgrief was arrested at a condominium in South Pattaya, while Brinkmann was arrested in Bangkok and taken to Nongprue Police Station in Chonburi.
Another German suspect identified as Enrico was arrested for operating a criminal account to receive a cash transfer from the victim.
A further suspect in the case is Nicole Frevel, a disabled German woman who rented the residence where the German businessman's remains were found. She was picked up in a restaurant near the condominium where Mack’s car was found and sent to Banglamung Hospital for treatment on a self-inflicted wound to the wrist.
Frevel told police that Brinkmann had brought the freezer to her residence and threatened her when she asked what it contained.
Deputy National Police chief Pol Maj-General Surachate Hakparn said Zahrouk is still on the run, adding that the suspects are part of a transnational criminal network involved in narcotics that uses Thailand as a base for the activities.
It is thought that the group had been preparing to rob Mack of his 3 million baht for about a month.
He said the stolen cash was transferred to about 10 criminal accounts and the police would be issuing arrest warrants for more criminal account operators as he believes that they are still in Thailand.
Surachate also vowed to instruct immigration police to deal with all transnational criminal networks in Pattaya and Nong Prue district to prevent further abduction cases.