Quote 1
A little strange, Fenerman thought, but it doesn't make the man a murderer. (5.51)
We wonder what it would have taken for Len to think someone was a suspect. If that someone was a seemingly respectable suburbanite, probably a heck of a lot. This also shows us that Len isn't one of those cops who uses 'gut feelings' to solve crimes.
Quote 2
"Each year it's something I do for Leah. […] My wife. I'm a widower." (5.54)
One big reason Len Fenerman buys the widower lie is because he himself is a widower. It's doubtful Harvey knows this; he's just being his creepy self.
Quote 3
"You remind me of my wife," Len said. (6.199)
Nice pickup line, Len. Although Len is dedicated to keeping families safe from bad guys, he does take his own swipe at the Salmon family. Abigail initiates the affair, but Len makes early advances.