An autopsy completed Wednesday confirmed the cause of death, Ingham County Medical Examiner Dean Sienko said.

Watson’s roommate, 20-year-old economics junior Shawn Wiltfong, suffered a broken rib, bruised lung and minor facial lacerations from the fall, said Brent Sielinski, president of Kappa Sigma Fraternity, of which Wiltfong is a member.

Wiltfong, the only passenger in the car, was released from the Sparrow Hospital Wednesday afternoon, a hospital official confirmed.

Before the crash, Watson and Wiltfong were driving to the Goodwill Retail Store, 6250 S. Cedar St., in Lansing, to get clothes for MTV Night, a Greek Week dance competition, Sielinski said.

The car was heading south on Cedar Street when it swerved off the four-lane road, catapulted into the air and landed in the middle of the Red Cedar, police said.

“I heard a loud bang and all of the sudden I had seen a car in the air,” said Ismael Guajardo, an employee at the Kwik Car Wash in Lansing, located a few hundred feet north of the river.

Lansing police Chief Mark Alley said there is “preliminary information” about what caused Watson to swerve the car, but he did not specify what type of evidence police have.

Tuesday night, Lansing police Sgt. Del Kostanko said a tire was flat when the car was pulled from the river a few hours after the crash. It is not known whether the flat tire contributed to the crash.

After the car plunged into the river, an off-duty Lansing police officer and Lansing resident Ryan Kowalk jumped into the river to help Watson and Wiltfong.

“When I arrived, (Wiltfong) was already on the roof of the vehicle and it was obvious he was in distress,” said Kowalk, 30, who suffered minor abrasions and lost his wedding ring during the rescue attempt. “Once he stated the fact that his roommate was in the vehicle, I knew somebody had to do something.”

Kowalk, who was at Kwik Car Wash before the crash, said he swam through about 20 yards of frigid water and pulled Watson out of the car. He then swam to the river shore with Watson, who appeared to be unconscious, and handed him to the three Lansing police officers on the scene.

After escaping from the car on his own, Wiltfong later swam to the shore and was transferred to Sparrow Hospital along with Watson, Lansing police Lt. Noel Garcia said.

Hospital employees worked to revive Watson for several hours before he was pronounced dead Tuesday evening.

Watson’s father and brother drove from their Chicago-area home and Wiltfong’s mother drove from her Flint home to Lansing after the accident, Sielinski said. Several friends and family members visited Wiltfong throughout the day, he said.

Funeral arrangements had not yet been made as of Wednesday afternoon, Sielinski said.

Staff writer Kyle Feldscher contributed to this report.