A nautical engineering trainee on Wednesday became the first crew member indicted in connection with the 20-ton, $1.1 billion cocaine seizure this summer at the Port of Philadelphia.

A federal grand jury has charged Nenad Ilić, 39, of Montenegro, with conspiring to violate maritime drug-smuggling laws — a count that carries a mandatory minimum sentence of 10 years should he be convicted.

His indictment offered the first public sign of progress since June in the investigation of what federal authorities have described as one of the largest cocaine busts in U.S. history. Since a splashy news conference at which law enforcement officials posed for photos next to stacks of seized cocaine, much of the probe has been carried out quietly and behind court sealing orders.

Wednesday’s court filings shed little new light on who smuggled the drugs aboard the MSC Gayane, the international vessel on which the illicit cargo was found, and made no claims as to how they did it or where the drugs eventually were bound.

However, the documents allege the effort involved multiple coconspirators as well as the use of “narco phones,” ski masks, fake shipping container seals, and threats of intimidation.

Ilić, whom court filings describe as an engineering cadet aboard the Gayane, was one of six crew members arrested shortly after the seizure. The five others remain in federal custody, but prosecutors declined to say Wednesday whether indictments against those men were forthcoming.

Court dockets show that a grand jury has issued at least two other indictments in the case, both of which remain under seal.

Ilić’s attorney Dennis J. Cogan was out of the country and could not be immediately reached for comment Wednesday.

After first detecting the Gayane’s illicit cargo as it docked in the Packer Avenue Marine Terminal in June, U.S. customs officials spent nearly a week searching the ship. They discovered drugs stashed in seven cargo containers carrying wine, vegetable extract, Chilean dried nuts, scrap metal, and other legitimate goods bound for Europe, Africa, and Asia.

According to now-sealed court filings obtained by The Inquirer, two other members of the Gayane’s crew — Fonofaavae Tiasaga, 28, and ship second mate Ivan Đurašević, 29 — confessed to involvement in the drug-smuggling operation.

They told investigators that they each accepted at least 50,000 euros (at least $55,000) to help secret the cocaine aboard. Both maintained they had done so at the direction of unnamed crew members.

The drugs, Tiasaga told investigators, originated on 14 boats that had approached the Gayane separately under cover of darkness during journeys between Panama and the Peruvian cast.

The other arrested crew members are Boško Marković, 27, Aleksandar Kavaja, 25, and Laauli Pulu, 32.

Prosecutors, meanwhile, have said they are still weighing whether to pursue civil or criminal forfeiture proceedings against the Gayane itself.

The ship was released back to its operator, Mediterranean Shipping Co. (MSC), in July after the Switzerland-based global shipping conglomerate posted $50 million in security deposits and surety bonds.

The company — along with the ship’s registered owner, Bermuda-based Meridian 7 Ltd. — also agreed to submit to the jurisdiction of U.S. courts while the Justice Department’s investigation continues and to refrain from retaliating against any employee whose testimony might damage their firms.

A spokesperson for MSC has said the firm has cooperated fully with the investigation.