Doink the Clown -- Autopsy Complete

The mystery into the death of Doink the Clown could be SOLVED in the next week ... 'cause officials have completed the autopsy on the ex-WWE star and are expecting results in a matter of days.

After Doink passed away Friday in Plano, Texas ... officials launched a homicide investigation into his death.

One law enforcement source tells us it appears Doink's death was "accidental" ... but the source wouldn't say if investigators believe drugs were involved.

The Plano Police Department tells TMZ ... its lips are sealed on the case until the investigation is complete ... which could happen as early as next week.