Coast Guard hearings into a collision on the Mississippi River that caused a major oil spill and closed the river for six days were expected to resume Thursday.

The hearings in federal court are examining an early morning collision on July 23 between a towboat pushing a fuel barge and a tanker. The fuel barge broke open, spilling 276,000 gallons of heavy oil.

The Coast Guard has said the towboat was under the control of an apprentice steersman, John Paul Bavaret II, and that the required licensed captain was not in the wheelhouse with him. The assigned captain was Terry Carver.

The Coast Guard has focused on the towboat operator, DRD Towing, by boarding its fleet to make sure its personnel were properly licensed and that its boats were safe. The Coast Guard did not find any major violations.

Less than two weeks before the July 23 collision, another boat operated by DRD was involved in a wreck on the Mississippi River while an apprentice mate was in charge, the Coast Guard said.

DRD officials and the towboat crew have not testified yet and it was unclear Wednesday who was expected to take the stand Thursday.

In August, the tanker’s Swedish captain, Jan Stefan Bjarve, testified that the towboat, the Mel Oliver, unexpectedly turned right in front of his ship. His ship, the Tintomara, had a special river pilot aboard, as required.

Federal prosecutors could file criminal charges.

The spill forced the Coast Guard to close 100 miles of the Mississippi, one of the busiest ports in the world.

At least one civil lawsuit has been filed, claiming people were hurt by breathing oil fumes.