Police had earlier identified 25 officers of the 2015 batch who had bribed APSC officials to get jobs through doctored answer scripts.
Of the 25 officials, 13 are in Assam Civil Services, seven are in Assam Police Services and the rest are in allied civil services.
"We have arrested 21 serving civil services officials so far. All of them have been sent to 14-day police remand. Further probe is on," Sahay told PTI.
Police had on November 8 arrested 16 civil services officials in connection with the cash-for-job scam in the tainted APSC in one of the biggest crackdowns against corruption in the state in recent times.
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The DGP said the probe was going in the right direction in the "most transparent" manner unearthing "reliable, admissible and acceptable" evidence.
Former APSC chairman Rakesh Kumar Paul was arrested on November 4 last year after the arrest of its two members -- Samedur Rahman and Basanta Kumar Doley.
APSC Assistant Controller of Examinations Pabitra Kaibarta was nabbed later.
Sahay had earlier informed that at least Rs 50 lakh in cash was seized from Paul and some of his "benami" properties identified.