Maineri was at a bar in Murrells Inlet, SC, when he was assaulted, according to WTNH-TV.
South Carolina deputies have charged 21-year-old Kelton Jess Todd with assault. Further charges are pending as the investigation remains ongoing.
Mainieri was a 20-year employee of the department, having begun working as a Community Service Officer in January 1998 and becoming a police officer in May 1999. During his career, Mainieri served as an officer, corporal, and sergeant. He served in the Traffic Division and Detective Division. He was a member of the regional traffic unit and was an accident reconstructionist.
"He was also an outstanding instructor in many areas including firearms and motorcycle instructor. He was a member of our regional emergency services team (C.R.E.S.T.) and was skilled at explosive breaching," the department said.
In recent months, Mainieri became heavily involved in starting a drone program for the department and obtaining the drone technology to find missing persons and suspects.