"I have been staking out this bakery for three hours, and my prime suspect hasn't shown up. It's frustrating because I have known since yesterday that he is the notorious muffin thief."

Use the Present Perfect Continuous (have been staking out) to talk about an action that started in the past and is still continuing now, emphasizing the duration (three hours).

Use the Present Perfect Simple (have known) with stative verbs like know, believe, or like. We do not normally use stative verbs in continuous tenses.