>> by her own actions, amy made her children witness this, to their father's murder. that, to me, is horrific. the mere fact that we would have to use them as witnesses against their mother was appalling. and she did that. she's the one that did that. up next, a family vacation turns to a nightmare. >> that's when i see the body of a female lying face down in the water. >> and possible clues provide more questions than answers. >> either it was an accident, someone caused her death, or she killed herself. >> experts can't seem to agree on exactly what happened. >> there is not one single eyewitness to anything. there are no confessions. there are no fingerprints. >> until groundbreaking science discovers the truth. >> method, opportunity, motive, and last person to see them alive. classic reasons for murder.