"They were good neighbors. He let me borrow his rake, once. I can't believe he'd hurt a fly."
"He seemed like a nice man. He never hollored or anything."
"He was always pleaseant. He never gave any indication he was capable of violence."
I'm sure there can always be more. But, this is usually the kind of lines repeated by everyone in contact with a serial killer or mass murderer.
You forgot "he was quiet and kept to himself"!