Diluc installed the light bulb, and then started to make a list of suspects that could've cursed Jean:
- Raiden Shogun
- Donna
- Kaeya
- Hu Tao
Why did he think these were the most suspicious people? Well first, Raiden. She just seems evil. Donna, of course she is in the suspect list. She tried to kill Jean twice. Kaeya. Because he poisoned Jean before. Hu Tao, she interacts with Jean too much. But he has to be tactical if he wants to achieve this. Since Diluc is also in the range of the light bulb, just one question like 'Why do you ask?' and he is screwed. So Diluc came up with a plan.
- Jean, wake up.
Diluc gently nudged Jean as she stirred in her sleep.
- What..?
She mumbled.
- Can you do me a favor real quick?
- Okay...
Jean got up and stretched. Diluc handed her a piece of paper and she read through it.
- What is this?
- I just want you to ask some questions.
- Alright?
She stood up and walked downstairs.
- Hi, Jean!
Hu Tao gleefully waved. Jean smiled warmly at Hu Tao.
- Hello. Do you mind if I ask you some questions?
- Sure!
Diluc watched as Hu Tao unhesitatingly answer to all the questions that he wrote down for Jean to ask. So turns out it wasn't Hu Tao. Of course, why was she in his list in the first place? Interacting with Jean too much is a ridiculous reason to put her in his list. Hu Tao did multiple times ask why Jean was asking these questions, but since Jean didn't know anything about why she was asking those questions, it would be the truth that Jean would just reply to them as 'I don't know'. The next person was the Raiden Shogun. He asked her to come, but she insisted on bringing someone with her. And that person made it very hard for Jean to interrogate Raiden.
- Why are you asking these questions?
- I already told you. I don't know why.
- That is an obvious lie. You wouldn't make up these questions if you didn't know why!
Diluc also did tell Jean to not reveal that Diluc gave her these questions, and she did a pretty good job of hiding it even though she was being called out for something she didn't write.
- Sara! Stop! I will answer these questions.
Raiden snapped. And that triggered Jean's curse. After Raiden said it, Jean immediately coughed out blood.