City CID chief Senior Asst Comm Datuk Zainuddin Ahmad confirmed that security guard Viswanath Murugaya, 25, was arrested last night after a tip-off from the public.
Vishwanath is one of the two people sought by police to assist in the murder investigations.
On Saturday, police released photos of Vishwanath and Dinishwaran a/l Raman, 23, whose last known address is at Batu Pekaka Estate in Kedah.
Anyone with information on their whereabouts can call Sentul police headquarters at 03-40482222 or investigating officer ASP Wan Abdullah Wan Said at 012-3482737.
The DNA test performed on the body found in a cemented oil drum on Sept 16 in Subang Jaya matched that of Morais.
Police were led to the location of the oil drum by a suspect who was among seven people remanded in the case, including an army doctor who was charged with engaging in unlawful trade while being a government servant.
The doctor has several corruption cases pending against him. Three DPPs, including Morais, had been involved in prosecuting the cases involving the doctor since 2013.
Morais went missing on Sept 4 after leaving his residence in Menara Duta here for work in Putrajaya in a grey Proton Perdana bearing registration plate WA6264Q.