ENGLEWOOD, Colo. -- Former Denver Broncos wide receiver Demaryius Thomas died from "complications of a seizure disorder," according to an autopsy report from the Fulton County (Ga.) Medical Examiner's office.

Portions of the report were shared with ESPN on Friday. Thomas was found dead in his Roswell, Georgia, home on Dec. 9 at age 33, and an autopsy was performed the following day.

In December, the medical examiner's office released a statement that "the cause and manner of death are pending the completion of laboratory studies and microscopic tissue samples." In the final report, the medical examiner said the manner of Thomas' death remains undetermined and it was unknown if the seizure disorder was the result of natural causes or due to impacts to Thomas' head during his NFL career.

Last month, researchers at Boston University told ABC News that Thomas had suffered from chronic traumatic encephalopathy (CTE), a degenerative brain disease, but said that CTE had not caused his death. The autopsy report said those same researchers said they did not believe Thomas' CTE caused the seizure disorder.

The autopsy report revealed that Thomas, who was found dead in the shower, had traces of nicotine and marijuana in his system, but neither was listed as a contributing factor in his death.

At the time of his death, some of Thomas' family members said publicly he had suffered seizures for about a year before he died. Several former teammates also said at the time that Thomas had told them he had suffered seizures in recent months.

Thomas' trademark smile and ever-present desire to help those in need made him one of the franchise's most popular players in the community. His death sent shock waves through the NFL and Denver.

Thomas, who would have turned 34 on Christmas, had announced his retirement from the NFL in June 2021 with a short video in which he flashed a peace sign and a smile.

Thomas was the first of two first-round picks for the Broncos in the 2010 NFL draft -- Tim Tebow was the other -- and spent nine seasons with the team. He finished his career as the Broncos' second-leading receiver (9,055 yards), behind Rod Smith. He is third in franchise history in catches (655) behind Smith and Hall of Famer Shannon Sharpe.

Thomas played in 10 seasons overall with the Broncos, Houston Texans and New York Jets and finished with 724 catches for 9,763 yards and 63 touchdowns.