Rainey, 54, was beaten to death in his second floor office in a strip mall on the 9200 block of Venice Boulevard in Palms in May of 2012.
Investigators say his murder was especially vicious. He had a broken jaw and his teeth had been kicked in. His wallet was stolen, but the motive for his murder remains unclear.
Rainey had more than 20 years of experience as a chiropractor and posted a number of informational videos to YouTube. He is also the brother of L.A. Times media critic James Rainey and the son of character actor Ford Rainey.
A $50,000 reward is being offered in the case, but witnesses have yet to step forward with information on his killer.
Rainey's family believes somebody knows something.
"Please, please come forward and help us to apprehend the person or persons that killed my big brother Robert," his sister said.
Anyone with information on this case was urged to contact the LAPD tip line at (877) LAPD-247.