Upvote:2
The short answer to your question is "Nobody knows who murdered Elizabeth Short".
A lot of theories have been advanced over the years, and several suspects have been named. Patrick S. O'Reilly is certainly one of the names that has been advanced as a suspect, but it seems that it was actually George Hodel who topped the LAPDβs list of suspects at the time of the crime. Hodel's son became a detective in the LAPD and has published much of the 'evidence' that he believes confirms his father's guilt.
As for other similar or related murders, a few have been suggested, but none with entirely convincing evidence to support the link.
You can read a lot of the background information about the case on the Black Dahlia website, and the unclassified FBI files are certainly worth reading too.