Macbeth's murder against King Duncan raises suspicion early on. Malcolm and Donelbain do not even want to stay at the castle longer than necessary and leave as soon as possible, because they suspect one of the lords at the castle. Really it is Macbeth's trail of crimes that incriminate him the most: first Duncan, then Banquo, and then most most obviously MacDuff's entire family. Malcolm and MacDuff are together in England when they hear of Macbeth's evil deeds, and both swear to remove Macbeth from the throne. Even Macbeth's own forces begin to doubt him at the very end, as Angus, who has joined the rebels, comments:
"Now does he feel
His secret murders sticking on his hands,
Now minutely revolts upbraid his faith-breach;
Those he commands move only in command,
Nothing in love" (V.ii.19-23).
Macbeth really contributed to his own undoing by committing too many murders; perhaps if he had only murdered Duncan, he might have gotten away with it, but his own ambition and personal greed for power led him to commit too many murders, thus contributing to his ultimate demise.