Onto the right track
Our story starts in the Defence Against the Dark Arts classroom. Alecto and Amycus are discussing the investigation into who has been trying to get them to quit their jobs.
Alecto said, "McGonagall told me that she's narrowed the culprit down to three suspects."
Amycus nodded. "Yeah, but we still need to narrow it down to the culprit from those three though. Remind me, who are the suspects again?"
Alecto told him, "1st year Gryffindor Spencer Dawson, 3rd year Slytherin Hanna Greaves and 4th year Ravenclaw Simon Johnson."
Amycus replied, "Hm, okay."
Alecto asked, "Any idea which it could be, Am?"
Amycus shrugged. "I'm not sure, my instinct tells me that it must be the Slytherin. It could be any of them though."
Alecto muttered, "Wait a second though. Where do I know the name Spencer Dawson from...?"
Recognition dawned on Amycus' face, he gasped. "Was that the first year who had something funny as a Boggart? What was it again, Ally?"
Alecto grinned. "A flying saucer, that's what it was."
Amycus smiled slightly. "That's the one, the whole class couldn't stop laughing at him."
Alecto went on, "We had to stop the whole lesson for that day because nobody could focus again."
Amycus inquired, "He has a decent motive for wanting us fired. It must be him then, right?"
Alecto nodded. "Yeah, I would certainly say so. Let's go tell McGonagall."