A Staten Island dad is threatening to sue Brooklyn DA Charles Hynes, saying his office botched a case against an allegedly sadistic bus matron who taunted his mute autistic son as the boy bashed his own head against a window.

“It’s an absolute disgrace,” Paul Rossi said yesterday after meeting with lawyers to review possible civil action.

The matron, Connie Clark, walked free this week after prosecutors missed a paperwork filing deadline by months.

A DA spokesman declined to comment. In papers, the DA blamed a change of address by Clark’s lawyers.

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