HPD officers were called out to 10110 Forum Park near Sugar Branch Drive just after 1:30 p.m. for a welfare check.
"Upon their arrival, they could smell the odor of what they believed a body coming inside the residence," Det. James Wallschlaeger said.
A neighbor reported having smelled a foul odor and noticed mail outside the unit that had been there for quite some time, HPD said.
"There was a weird smell, blood coming through the porch from the back, and the smell was from about three days," a neighbor, said.
HPD said the two adults were reportedly in a dating relationship.
Investigators say the cause of death appears to be from a gunshot.
According to investigators, no motive has been determined as the investigation remains ongoing.