Oklahoma authorities are searching for a suspect after four people were found dead and another person injured at a marijuana growing operation in Kingfisher County Sunday night, according to the state’s bureau of investigation.

The Oklahoma State Bureau of Investigation said the three men and one woman – all Chinese nationals – were executed, and that their deaths were not a random incident, according to a news release from the bureau.

The Kingfisher County Sheriff’s Department responded to a reported hostage situation Sunday and found the victims when they arrived, Capt. Stan Florence with the Oklahoma Bureau of Investigation said Monday.

The injured person – also a Chinese national – was flown to an Oklahoma City hospital for treatment, but Florence said he did not know their current status.

Florence said authorities “have a suspect in mind” but after a search throughout the night with investigators on the ground, drones and helicopters they don’t believe the suspect is still in the area. Investigators are not yet releasing the identity of the suspect, saying that doing so would “put additional individuals in danger,” the bureau of investigations news release said.

Investigators are trying to piece together what happened, Florence said, but believe the victims and suspect knew each other.

“They all know each other. [We] don’t know if they’re related, don’t know if they’re coworkers, but certainly these individuals were, we believe, all familiar with each other,” Florence said.

The Oklahoma Bureau of Narcotics is also on the scene to investigate the growing operation, according to Florence. It was not immediately clear if the operation was legal and licensed. Medical marijuana is legal in Oklahoma.

Kingfisher County is northwest of Oklahoma City.