my husband's cousin Cindy (who was a widow) married a guy who killed his second wife this same way... pushing her off a hiking trail... Cindy was his fourth wife and did not know this guy's background... all she knew was that he was a widower, and she thought she was his second wife... anyway, he killed Cindy by drowning her at a lake, while her two young sons and his son waited for them at the shore... his name is Randy Roth... he is in prison in Washington... Ann Rule wrote a book called A Rose for Her Grave, and this story is in that book...
you can look google Randy Roth... diabolical, indeed...