The Bureau of Alcohol, Tobacco and Firearms is looking into the cause of the fire.
It happened Thursday at Garden Ridge on the North Freeway and Texas 242 in Conroe.
The blaze caused an estimated $15 million in damage.
The ATF say it needs witnesses to come forward.
Federal investigators want to talk to anyone who might have been in or near the Garden Ridge store last week. They're looking to talk to anyone who they have not already interviewed.
Investigators say the flames appear to have started near the middle of the store. They spread quickly. Between two and three dozen customers were inside the store at the time, along with 23 employees.
Everyone was able to escape.
ATF agents say they've only been able to talk to a few of those folks.
"What we're hoping is that they can tell us what they saw at the time of the fire inside the store. That, along with what we found inside the store, can hopefully give us some idea as to the origin and cause to this fire," Franceska Perot with ATF said.
The store had a sprinkler system, but the intensity of the fire apparently overwhelmed it. There was only one minor injury -- a case of smoke inhalation due to the fire.
If you were at or near the store on Thursday and have not spoken to investigators, you are urged to call ATF at 888-ATF-FIRE or 888-283-3473.
Investigators are not saying whether they believe this fire was intentionally set, but they are not ruling anything out.