thinking when you hear that? >> well, i'm thinking a couple things. i'm thinking, "that's gonna be a problem at trial because of the contamination." but i'm also thinking, "thank god, we get a little break. >> reporter: and after all the additional testing, the medical examiner finally had a cause of death, acute midazolam poisoning. investigators took everything they had to a special prosecutor and argued they were sure gilberto nunez had killed the man he called his best friend. >> i don't think that nunez was ever a friend to kolman. not for a minute do i believe that. he is a master manipulator. he lives to manipulate. i believe he drew tom in because he wanted to be closer to the wife and have access to the wife. >> reporter: nearly four years after tom's death, gilberto nunez was indicted for second-degree murder. how did that feel when you got that news? >> i cried. we all cried pretty hard. it felt -- it felt good in that, you know, we're one step closer to justice for tom. >> reporter: but tough times were still ahead for linda. at trial, prosecutors were about to reveal new details about her affair. coming up -- another stunning affair. undercover agent? when the good husband continues. undercover agent when the good husband continues. y 'what ifs' were erased.