Rainey, 54, was found beaten to death in his chiropractic office in the Palms neighborhood on May 31. Investigators said Rainey had a broken jaw and his teeth had been kicked in. He was found by a patient in his second-floor office in a strip mall on the 9200 block of Venice Boulevard.
Rainey was rushed to a hospital where he died a short time later. Investigators said they only have a vague description of a man with a pipe or bat spotted in the area. Robbery was a suspected motive.
"Whatever the motivation is, we just need one person to come forward with that one tidbit of information that helps us," said LAPD Captain John Peters.
Surveillance cameras in the area did not capture an image of a suspect.
"There are some cameras here that ideally would have been functional and probably would have caught the perpetrator, but unfortunately thus far we have nothing on video," said LAPD Lt. John Radtke.
Rainey had more than 20 years' experience as a chiropractor and posted a number of informational videos to YouTube. He is the brother of L.A. Times media critic James Rainey and the son of character actor Ford Rainey.
"He was a character. He had a big booming voice and he was full of life. So it's a tremendous loss," said James Rainey at Thursday's news conference.
Anyone with information about the case should contact the LAPD at (877) LAPD-247.