Answer:
"It seems as if Malcolm and Donalbain left Scotland due to fear after seeing Duncan dead. Both of them were close to Duncan, and they believe that it is possible they may get targeted as well, by the person who ended up killing Duncan in the first place. Doing so also allows the people and citizens to believe that it was their fault for the Death in the first place, creating a path for Macbeth's succession to the throne. Dunablain says, "To Ireland, I. Our separate fortune shall keep us both the safer. Where we are, there's daggers in men's smiles. The near in blood/The nearer bloody" (2.3.8). This shows that the two men are afraid even their own relatives will kill them. "
Step-by-step explanation:
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(They leave because they fear that, as close male relatives of Duncan's with strong claims to the Scottish throne, they will be targets of whatever person murdered Duncan. However, their suspicious flight allows the Macbeths to suggest that they are behind Duncan's murder, as Macduff's remark in Act II, Scene iv, lines 24-27 indicates.)