The police was checking a place. Outside, Bambam, Mr. Kim's faithful secretary was a mass of nerves. Inspector Youngjae was reviewing the facts:

1. Mr. Kim has been murdered. The murderer buried a stiletto through the back of the chair and right through his heart.

2. The place was a mess, but nothing seems to be lost. Some sheets on his desk had coffee stains but Mr. Kim was not a coffee drinker. There was no coffee container of any kind in the office. There was a couple of gloves in the floor.

3. Bambam had in his visit book just three announcements. Im Jaebum (1:32), Mark Tuan (3:15) and Jackson Wang (3:50). Bambam says that Jackson was the only one to serve himself a cup of coffee in a paper cup.

4. The cup of coffee was found in Bambam's wastebasket. He claims that Jackson entered Mr. Kim's office with the cup in his hands and then he left it in Bambam's desk, so Bambam took it and threw it away.

5. The stiletto had no fingerprints at all, but the paper cup was all covered with one type of fingerprint: Jackson's.

6. Mr. Kim's wristwatch was broken, probably due to the fight, and it showed the time at 3:58.

Inspector Youngjae then talked to Bambam to tell him he was under arrest. Why did he suspect him?