It all happened at about 2:49 p.m. along the 4500 block of FM 1960 E.
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Texas DPS said they were tipped off with credible information about the grenade, which may be linked to an ongoing investigation.
Authorities conducted a traffic stop and found the grenade in the vehicle. After that, the Harris County Sheriff's Office Bomb Unit responded but later rendered the item safe.
The driver of the vehicle was taken into custody. Details regarding the second person charged were not immediately available.
This case remains under investigation.