PLEASANT HILL -- Officials are hoping a $5,000 reward will entice a witness to come forward in the case of a Diablo Valley College police services officer who was injured by an unknown assailant while on duty.

Trina Gaines, a five-year veteran of the department, was posted near a parking lot off Golf Club Road around 9 a.m. Dec. 3 when she was suddenly struck in the face with a small metallic object, according to Timothy Leong, spokesman for the Contra Costa Community College District. She fell to the ground and was bleeding from the face, Leong added.

Pleasant Hill police responded and called an ambulance, which took Gaines to a hospital in Walnut Creek. She is recovering at home and is still off-duty, Leong said.

Investigators are still trying to figure out what the object was, Leong said.

"We think there must have been some students that were in the area that may know something," Leong said, "so we're trying to use this reward as hopefully an incentive to encourage students (to come forward.)"

Anyone with information about the incident is asked to call police services at 925-685-1230, ext. 2338. Anonymous tips can be submitted at ext. 1999.

Contact Daniel M. Jimenez at djimenez@bayareanewsgroup.com. Follow him at Twitter.com/DMJreports.