in february 2018, the waters of lake coeur d'alene were holding fast onto larry isenberg. d lori had launched their romantic sunrise cruise here at sun up bay and headed for the big resort up the top of the lake, 16 miles away. but four or five miles in, around powderhorn bay, right about here, said lori, larry went to fix something in the bow and then looked around at her and turned a deathly shade of gray. and-- the initial responders, they felt fairly confident that it was another tragedy out on the lake. keith morrison: a semiretired detective named brad maskell heard about it, of course, like everybody in town. he was just an observer, but he knew a thing or two about the lake. he lived here most of his life. water that cold and that deep around that middle of the lake, would you expect his body to sink right down to the bottom? typically, in cold water environments like we have, and deep water environments, yes, you immediately submerge, and the body very typically will go to the bottom. and when you go down at depth, let's say, 90 to 100 feet or deeper, it's very rar

i just remember him as the immortal larry isenberg that he always was. i don't have to have the memory of him getting sick and frail and slowly slipping away, helpless in a hospital bed. i get to have nothing but the good memories of him. keith morrison: larry isenberg, that honest man, whose fatal flaw was to love the woman who couldn't be. . i'm craig melvin. and i'm natalie morales. and this is "dateline." michelle's dead. how is that possible? craig melvin: a young mother found brutally murdered-- >>> >>> police had a suspect, and they say he had a motive. we had an intimate relationship. we ended up having sex. craig melvin: but could they prove he was the killer? it was a circumstantial case. craig melvin: except for that witness-- the girl who left those footprints. fiona childs: we will never know what cassidey saw and what she didn't see. craig melvin: maybe she couldn't tell detectives who the killer was, but maybe she didn't have to. the fact that cassidy was spared-- would that mean anything to a jury? becky holt: the person that killed the m