But prosecutors also said Wednesday that questions had arisen about unusual financial transactions by the grandfather and father.
Chief financial investigator Santiago Nieto said that “the financial irregularities concern income from possible money laundering and tax evasion.”
Local media reported the boy lived with his grandmother because his mother had been killed and his father had been in jail for drug trafficking. Authorities have not confirmed those reports.
Officials are prevented by law from even fully identifying the suspects, expect by their first names. All three generations — grandfather, father and boy — shared the names José Angel.
During Friday’s shooting, the boy also wounded six others at the school in the northern city of Torreon. All are expected to survive.
Such school shootings are extremely rare in Mexico, but drug gang violence is common.
Coahuila Gov. Miguel Riquelme said it appeared the grandfather did not have permits for either weapon.
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