In this passage there is a slight pause after 'must' and a stress on 'not':
'I saw Isabella she had a blank expression on her face. I'm not sure what happened with the knife she was carrying it looked like she was still holding on to it, and I looked down and I saw my wife on the floor blood everywhere all over the bathroom. I was talking to the dispatcher and the dispatcher told me, 'Make sure you get her breathing again. Get her airways open.' I don't know CPR so... But at that time I looked at my wife's eyes and I knew that she must not have made it. I just couldn't, couldn't believe that, that it had happened like that. Isabella was in a rage like I've never seen before.'
(from an interrogation of Ryan Hoy, Youtube video 'When An Insane Teen Killer Makes Detectives Snap')
Would there have been any difference in meaning if he had said, '...she mustn't have made it' or 'she must have not made it' instead?