OAKLAND (CBS SF) — An Alameda-based U.S. Coast Guard commander has pleaded guilty to drug trafficking charges involving the importation of a controlled pain killer from foreigner suppliers, federal prosecutors have announced.

U.S. Attorney Dave Anderson said James Heyward Silcox III has pleaded guilty to all three counts in the federal indictment. He will face a possible sentence of 5 years in prison and a fine of $250,000 for each count.

READ MORE: Kevin Nishita's Only Daughter Opens Up After Fatal Shooting; 'He Doesn't Want Us To Be Sad'

The case centered on the illegal importation of a drug called Tramadol — a powerful pain killer only legally available with a doctor’s prescription.

Silcox, 42, was originally charged on September 18, 2019 in a complaint that alleged he illegally imported Tramadol from Singapore and Germany to post office boxes he held.

During the change of plea hearing, the government advised the court of evidence that Silcox began purchasing tramadol in 2017 online from an unknown person he believed was in Singapore. The government offered further evidence that Silcox had received shipments of tramadol from three separate overseas suppliers from 2017 to 2019 and sent shipments to downstream buyers of 500-1000 pills per month.

READ MORE: Theranos Trial: Tears Flow As Elizabeth Holmes Talks Of Fractured Love Affair With Sunny Balwani

According to the complaint, in July 2019, Customs and Border Protection officers at the JFK International Air Mail Facility inspected a package from Singapore that contained approximately 865 grams of Tramadol.

In August 2019, CBP officers at the San Francisco Air Mail Facility intercepted a package from Germany that contained 650 tablets containing Tramadol.

And on September 13, 2019, CBP officers in the San Francisco Air Mail Facility intercepted a package from Singapore that contained 458 grams of Tramadol.

All three packages were addressed to post office boxes held by Silcox.

MORE NEWS: Man Charged With 4 Felonies In Danville, San Ramon Robbery Crime Spree

According to the government, Silcox used end-to-end encrypted communication applications and email services to communicate with his overseas suppliers and his downstream domestic customers and used crytpocurrency to make payments.