"Skyjack" author Gray says the hijacker was positively giddy and childish (as described by one of the flight attendants) when he got the money. So, not always quiet and efficient. Not always in character.
DNA results for LD Cooper are inconclusive thus far. He's not "ruled out."
"No match" in this situation simply means "no positive identification." It doesn't mean there's a negative relationship between the samples. DNA sampling can't accomplish much in this case unless they find the butts.