A member of the Mormon family murdered in Mexico has accused the local authorities of complicity in the killings, mocking their claims that they took 10 hours to arrive on the scene because they didn't have enough petrol.
Julian LeBaron, who has urged Mexico's president to accept US offers for help in investigating Monday's massacre, said he had no faith in the local authorities.
"The governments of Sonora and Chihuahua states are complicit in this murder," he said.
"I do not believe that the authorities will be able to secure justice. They are corrupted down to their bone marrow. They told us they couldn't get to us because they didn't have enough petrol - it's that level of stupidity."
Mexico has for decades wrestled with corruption. Wealthy drug cartels will bribe poorly-paid local officials to turn a blind eye to their activities, enabling the cartels to traffic drugs and murder with impunity.
Andres Manuel Lopez Obrador, Mexico's president, has sent a team to investigate, but few are confident of any arrests.
Adrian LeBaron, whose daughter Rhonita, 31, and four of her children died in the massacre, further said he did not believe the government's suggestion that the Mormon cars were mistaken for the vehicles of cartel members.
Three adult women and six children died in the hail of 200 bullets. Seven other youngsters - the oldest aged 14, the youngest a seven-month-old baby - survived, and Mr LeBaron said the children had told him they could not have been mistaken as drug cartel members.
One of the women came out of her car with her hands raised, Mr LeBaron said he had been told.
He also told CNN's Spanish affiliate that the family had been threatened recently by the organised crime groups operating in the area.
"We are from one of the most productive families in the area," he said, speculating that the cartels wanted to "send a message".
"This was not an accident. This was not an error," he said.
Mr LeBaron said he had received menacing telephone calls warning them not to be "nosy" in cartel affairs.
"A few months ago there was an incident where some petrol was stolen. They get upset when you buy your own petrol, because they think it's their own domain, and they made some threats.
"We got some calls, warning us not to be gossips, saying that they wouldn't bother us. And then they gunned down three families."