In two films about the Titanic, Murdoch was portrayed shooting passengers and himself during the sinking; this was based on a number of eyewitness testimonies of a shooting/suicide by an officer during the launching of the last lifeboat. It is possible that Murdoch was the officer.
In general, to append is to join or add on to the end of something. For example, an appendix is a section appended (added to the end) of a document. In computer programming, append is the name of a procedure for concatenating (linked) lists or arrays in some high-level programming languages.
Meaning to hang on, attach as a pendant is 1640s; that of attach as an appendix is recorded by 1843. OED says the original word was obsolete by c.1500, and these later transitive senses represent a reborrowing from Latin or French. Related: Appended; appending.