Houston police responded to two scenes -- 6200 Luce Street and 6200 Nunn Street -- just after 10 p.m. Wednesday after receiving multiple reports of a shooting in progress.
When officers arrived at the home on Luce Street, they found a man wearing a mask dead in the driveway.
Officers went into the home, where they found a second man dead and a third man with a gunshot wound.
A fourth victim was found with a gunshot wound in a house on Nunn Street, which is right behind the Luce Street home.
Investigators believe there was an exchange of gunfire based on the casings found inside the home. They also believe it was drug-related because there were narcotics in plain view inside the home on Luce Street.
It's unclear if it was a narcotics-related robbery or a drug transaction gone bad, HPD said.
The two gunshot wound victims were taken to the hospital in stable condition.
Homicide investigators are continuing to review evidence at the scene, including surveillance video from inside the residence and from neighbors.
Police believe all four men were between 20 and 30 years old.
Investigators said more possible suspects may have fled the scene.
"There are conflicting reports about whether there are other suspects. It's likely that there are perhaps three others, but we don't know if they left on foot or in a vehicle," Asst. Chief Jessica Anderson said.