The violent slayings of nine men at a drug house in northern Mexico were motived by a debt of about $460, officials said Wednesday.

The weekend killings in the Apodaca suburb of the northern city of Monterrey shocked area residents. The victims were bound, and two appeared to have been stabbed while the other seven were strangled.

Apodaca Mayor Oscar Cantu was briefed on the investigation Wednesday by state prosecutor Roberto Flores.

"It had to do with drug consumption," Cantu said. "It was a very small debt these people had. It is a very shocking thing."

Cantu said one man survived the attack over the weekend and has provided investigators with key information.

The man survived by playing dead. The fact that he survived was not previously acknowledged in an effort to protect his security.

Two suspects have been arrested in the killings.

Nuevo Leon state Gov. Jaime Rodriguez Calderon said Sunday that the initial investigation suggested the house was used for drug consumption.

The house where the killing occurred was the scene of another crime in 2014, when a 17-year-old stabbed his father to death as he fought with the young man's mother.