arkansas and stayed. never found out that tom moved away. i didn t feel like i could go back home to montana. reporter: why? because tom was there, and i thought if he was willing to kill somebody to be with me, i didn t know what he d do. reporter: corrosive. that s what it was. but then, 13 years after dr. rein s murder, this man got a new job. this is brant light, who in 2009 became the top prosecutor in the montana attorney general s office. and one of his duties was to help small counties prosecute particularly difficult cases. cold cases. we don t get the slam dunks turned over to us. we get the older cases. we get the difficult cases, and we re expected to go forward with those cases. reporter: like the one light s old friend ken thompson had never really given up on solving. so i felt comfortable to go to brandt and say would you just