A Bay Shore man was convicted Friday of sexually abusing a girl for four years, starting when she was 8, the Suffolk County District Attorney’s Office said.

A jury took 40 minutes to find Robert Kattau, 43, guilty of first-degree sexual conduct against a child, a violent felony, and endangering the welfare of a child, a misdemeanor, prosecutors said.

His Legal Aid attorney, David Geller of Riverhead, said the conviction will be appealed. “We don’t believe there was enough evidence to convict him,” he said.

The abuse started in summer 2012, and Kattau was arrested last March, after the victim told a friend, whose family notified school officials, authorities said.

But in a written confession, Kattau blamed the child victim for his conduct, said Robert Clifford, spokesman for District Attorney Thomas Spota.

Geller said Kattau did not write that confession. Often, police will summarize and write the suspect’s statements, have him or her read it, then sign it if they agree.

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“He said he was tricked,” the attorney said. “The officer wrote it, and he signed it, unfortunately.”

In a statement, Spota said prosecutors will seek the maximum sentence of 25 years in prison at the March 14 sentencing.