A Sagaponack man with a history of psychiatric problems pleaded guilty Tuesday to burning down the Water Mill mansion of a couple he knew.

David Osiecki, 65, pleaded guilty to third-degree arson in an unusual deal colored by his bipolar syndrome and other psychiatric issues. Assistant District Attorney Peter Timmons said his office and defense attorney William Ferris tried to reach a deal that will hold Osiecki responsible for what he did while trying to get him the help he needs.

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The deal requires Osiecki, who has been in jail for 13 months, to be evaluated at a psychiatric hospital and serve a year on probation. If he's successful on probation, Timmons said the charge will be reduced to third-degree attempted arson and Osiecki will serve another 5 years on probation.

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If he's not successful, state Supreme Court Justice Fernando Camacho will sentence him to 1 1/2 to 4 1/2 years in prison.

"I want to thank you for this creative treatment plan," Osiecki said to Camacho and Timmons.

"Mr. Osiecki, we're all very hopeful that you get the treatment you need," Camacho said.