On Sunday, a source says the officer was at a nearby lounge and put his hands on the bartender, hurting her.
A complaint was filed and the officer was put on paid administrative leave the same day.
"We have very clear policies and procedures for dealing with allegations that are brought forth," said Phil Comstock with the Lacey Police Department.
The bartender told KOMO 4 she is still a little shaken up to talk, but that she is happy the allegations turned into a criminal investigation.
Because this is a criminal case, it was turned over the Olympia police department today for outside investigation.
"They were requested to conduct the investigation, the criminal investigation for the Lacey Police Department," Comstock said.
The sergeant will stay on leave while Olympia police look into the complaint. Lacey will do its own internal review after that.