Kiesha Lockett, 39, was last seen in the Texas Medical Center on Aug. 17.
It's unclear if she was the person found in the car when it was discovered around 4 p.m. on Tuesday in a waterway under the East Freeway near Brookshire Street.
"It's unknown if that person's a male or female," Harris County Sheriff Ed Gonzalez said on Tuesday.
One man, who asked not to be identified, citing safety concerns, said a friend of his spotted the car while out picking up trash along the water, which he said had receded considerably from its normal levels.
He said she called him, and he came out to see the car for himself. On his way, he spotted a Harris County sheriff's deputy who was in the area on another call and led her to the car.
ORIGINAL REPORT: Vehicle found submerged in water in east Harris County may be tied to missing person's case: Sheriff
Body in submerged vehicle may be tied to missing persons case: Sheriff
"I just figured it was just somebody's dumping a stolen car," he said.
It wasn't until a tow truck had pulled the vehicle from the water that investigators discovered a body in one of the front seats.
The medical examiner's office told ABC13 on Wednesday that it still hadn't determined the gender of the person and hadn't yet made an identification.
Houston police initially told Eyewitness News it couldn't release any information related to the missing persons case.