New pieces of evidence are emerging after last week's massacre in Ohio that killed eight family members. 

Authorities have interviewed over 30 people but have yet to make any arrests, CBS News reported. 

Investigators found on Monday that the youngest member of the family killed in he massacre, Christopher Rhoden Jr., received a threat on Facebook days before the shooting, according to CBS. The message's content has not been revealed but it specifically targeted the 16-year-old. 

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"I'm aware of the Facebook threat," Ohio Attorney General Mike DeWine told CBS. "Every piece of information is valuable and our investigators are certainly taking that into consideration."

Authorities reportedly called it a "preplanned execution" on Sunday. DeWine said it will take a long time to investigate the "sophisticated operation." 

DeWine said that marijuana-growing operations were found on Sunday at three of the four crime scenes with about 200 plants, according to the New York Daily News, but added that there was not enough evidence yet to link it to the massacre. 

The size of the operation indicated to investigators that it was being grown for sale, not personal use. Each plant could reportedly produce a pound of marijuana, which has a street value of about $2,000.  

RELATED: Execution-style shooting in Ohio kills eight

A law enforcement source told CBS that multiple angles are being examined to determine a motive for the killings. Authorities are looking at a possible drug turf war or family feud and even whether there was a connection to the Mexican drug cartel. 

“This was very methodical," Pike County Sheriff Charles Reader said, according to the Daily News. "This was well-planned. This was not something that just happened." 

Three small children — two infants and a toddler — survived the attacks.