The Tarrant County Sheriff’s Office has released more details about Mack Greer’s death in June, following an outside investigation by Haltom City police.

Sheriff Bill Waybourn said the police investigation found that Greer died of natural causes linked to a genetic disorder. The county medical examiner reported last month that complications of moyamoya disease, which restricts blood flow to the brain, caused his death. Greer died June 18, two days after he was taken from the county jail to John Peter Smith Hospital.

Waybourn said he wanted to correct statements by County Commissioner Alisa Simmons, who said at a June 19 news conference with Greer’s parents that he may have suffered a fatal head injury before reaching the hospital. Greer’s parents, Lea and Jospeh Hurd, maintain that he suffered head injuries in custody and died from them. At least seven people have died in custody in Tarrant County this year.