Since homicides are crimes, and all crimes require either intent or negligence, it follows that some homicides require either intent or negligence.
This arrangement respects all conditions: L is in seat 1, M and N are not next to each other, and X is immediately to the left of W.
For the prosecution to succeed, all three elements must be proven. If one element is disproven, the case cannot be won.
Analyzing the logical chain, if Ellen is not on the case, Bob can be on it. If Bob is not on it, Carol can be. If Carol is on it, Dave must be. If Dave is on it, Alice cannot be. Therefore, Dave must be the one on the case.
By process of elimination, assuming only one person is guilty, C is the only person whose guilt does not contradict the conditions set forth.