A man has been arrested in connection with the deaths of four of his family members in the Casa Grande area, authorities said Monday.

Pinal County Sheriff's officials said 21-year-old Richard Wilson was booked into the county’s jail on suspicion of four counts of first-degree murder with his bond set at $2.5 million.

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They said deputies responded to a frantic 911 call Sunday afternoon and found four people dead inside a home.

Wilson was still at the scene and taken into custody. Authorities said a knife was allegedly used in the killings, but a possible motive wasn’t immediately known.

It was unclear Sunday if Wilson has a lawyer yet who can speak on his behalf.

Sheriff's officials said the victims have been identified as 47-year-old Richard Wilson, the suspect’s father; 50-year-old Ellen Otterman, the suspect’s mother; 16-year-old Rudy Wilson, the suspect’s sister; and 5-year-old Renaya White, the suspect’s niece.

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In a statement Monday, county Sheriff Mark Lamb called it "a terrible tragedy" and said "this act of depraved violence will have long-lasting effects on all those who knew this family."