Probably has more to do with mental illness than selfishness...just a guess.
Murder/suicide is always, IMO, based in a mental illness, temporary, accute, or chronic. However, IMO, it is still a selfish act.
self·ish
ˈselfiSH
adjective
(of a person, action, or motive) lacking consideration for others; concerned chiefly with one's own personal profit or pleasure.