The Crown has recommended a sentence of seven to nine months in the case of a Sydney police officer charged with obstruction of justice and breach of trust.

Const. Ron Williams was found guilty in November.

In 2011, a liquor inspector reported to police that an impaired driver was leaving the legion in Whitney Pier. The 39-year-old Williams was at the police lock-up when he was assigned the call.

Williams was charged after he asked the jailer to warn the alleged drunk driver by phone that police were on their way to his house and to not answer the door. Williams also falsified a police report about the incident.

No clear motive

Crown attorney Shauna MacDonald told the court it's still not clear why Williams did it.

"In some circumstances involving police officers, you'll see theft or drug dealing sometimes," ​she said.

"Where you can point to an obvious gain that they are financially motivated. We've had no indication of what the motive was behind it."

MacDonald suggested a sentence of seven to nine months, either in the community or in jail.

The defence recommended a conditional sentence that would allow Williams to keep working out west as a pipefitter.

Judge Simon MacDonald will give his sentencing decision Tuesday morning.

Williams, an 11-year veteran of the force, was suspended with pay on Aug. 3.