The Harris County Sheriff's Office said deputies responded to a home on Everington Drive just before 5 p.m. and found the man unresponsive with gunshot wounds in the passenger seat of a car parked inside the garage.
He was pronounced dead at the scene. Investigators said it appears the man was shot somewhere else and then driven to the home.
Inside the home, the sheriff's office said, was the 911 caller and her 23-year-old son.
HCSO said another 23-year-old man, a friend of the 911 caller's son, was the one who drove the shooting victim to the home and left before deputies arrived.
In a release, the sheriff's office said they interviewed witnesses and secured a search warrant that "led to incriminating evidence found inside the home."
After interviewing the 911 caller's son, deputies said they found inconsistencies with his statement and the evidence found.
The other man declined to provide a statement to detectives, HCSO added.
Anyone with information is asked to call the Harris County Sheriff's Office Homicide Unit at (713) 274-9100 or Houston Crime Stoppers at (713) 222-TIPS (8477).