PITTSBURGH — The city’s former police chief was sentenced to 18 months in prison for conspiring to create an unauthorized slush fund, with a federal judge saying she was sending a message that the seriousness of his crimes outweighed his supporters’ calls for leniency.

Nathan Harper, 61, also was ordered to repay $31,986 that he spent on himself, including meals and drink tabs at various restaurants and bars.

Harper resigned last February and in March was charged with conspiracy to commit theft and failing to file tax returns between 2008 and 2011, when much of the money was misappropriated.

Harper never denied wrongdoing, though his attorneys say the chief was ordered to start the slush fund by someone they refused to name. Eight family members and friends testified to his character Tuesday, each of them asking to keep Harper out of prison because of his otherwise spotless record and gentle demeanor.

Even Assistant U.S. Attorney Robert Cessar, who argued for the prison term, lauded Harper’s law enforcement work.

“If I were not here as an assistant U.S. attorney, I may well have been one of those people writing letters of support for Mr. Harper,” Cessar said, referencing more than 30 letters received by the court.

But U.S. District Judge Cathy Bissoon said a “slap on the wrist” would “send a dangerous message to the public.” She added, “Unfortunately, no amount of kind words can erase the seriousness of his crimes and the breach of public trust.”

Her sentence left the courtroom in stunned silence and Harper’s wife, Cynthia, and other relatives in tears.

The sentencing marked a striking fall for Harper. Harper joined the department in 1977 and was appointed chief in 2006 by the recently departed mayor, Luke Ravenstahl.