Watertown Retirement Board officials are seeking court documents that would help them decide whether to revoke the pension of a retired police sergeant who recently pleaded guilty to drug and fraud charges. During a federal court hearing on Aug. 13, Joseph Deignan, 58, of Framingham, admitted to stealing a driver’s license while he was a Police Department traffic supervisor in 2010, and using it to illegally obtain oxycodone and other prescription drugs, according to the office of US Attorney Carmen Ortiz. He was charged with unlawful possession of a controlled substance by fraud, and fraud in connection with identification documents, the prosecutor’s office said. Watertown officials said Deignan, who served on the police force for 32 years, has been collecting an annual pension of $55,731 since his retirement in February 2012. If Deignan’s convictions are found to relate to his former job, the board could move to take away his pension under state retirement law, including any money he has collected since the date of the crimes. Thomas Gibson, the retirement board’s lawyer, said Monday that he was directed to collect the court documents, such as the docket sheet, statement of case, and plea colloquy, to determine specifically what Deignan pleaded guilty to and when the crimes happened. Gibson said he will report his findings to the board at its next meeting, scheduled for Sept. 18. The board could then choose to hold a pension forfeiture hearing; Deignan would be issued a summons to attend the hearing, and would have 30 days to obtain a lawyer, Gibson said.