Police said that the arrests were based on CCTV footage and witness statements.
The suspects have been remanded until May 23.
Priyasad was fatally shot by an unidentified gunman last month while at his wife's residence, located in the Laksanda Sevana housing complex in Saalamulla in Wellampitiya.
Police noted that investigations have revealed a direct link between the assassination and the alleged criminal figure Kanjipani Imran.