During lunch, Sungmin was asking Kyuhyun why he deduced that the security guard must have something to do with the murders. Kyuhyun asked him instead "in your novel, was there a book left near the bodies, after each murder?" 

"No, but the murderer left a note". 

"Similarly, the murderer left your book with your signature next to your body. How did he gets your signature? Either, he's a fan of you and got your autograph during your signing event, or he knew you and asked from you. Now we know that he asked from you. Anyway, we have informed the airport services not to engage any 3rd party delivery services unless they got clearance from us. So, so far, the murders stop. Is it ok to tell me what are the murders about in your next novel series?". 

"Sure Kyuhyun, but it's something which I don't think the current murderer would follow. It's about a dentist, who's clients are rich people, and previously looked down on him when he were doing odd job labourers just to finance his studies. He implanted a toxic poison into the client's crown or bridges or tooth fillings, and when the fillings slowly eroded off, the toxic poison will be release and when he swallowed his food, the poison took effect and these clients will die due to excessive poison in blood plus diarrhoea and vomiting blood. The time frame between they got the poison implanted and the actual murders are long, so the dentist wasn't suspected, until the chief investigator started comparing which dentist these people go to, then they find the connections". 

"So gross and so complicated. Where did you get the idea from?"

"While I was having my tooth pulled out actually, haha"

"Wow, novelist like you can get ideas almost from anywhere. Ok, so will it be ok if you hold launching your 2nd series of novel first? Will it go against your contract or something?". 

"No, it's ok. I already told them I'm helping the police with investigation".

"Great. I don't want to be the cause of you losing or getting your contract with your publisher terminated". 

"Don't worry, I won't blame you even if that happens. You are my life saviour. I owe you a lot". 

"I'm not. I'm just ensuring your safety". 

"Yes by giving me personal protection! You can just get police officers to guard my door"

"Why, you don't like it? I just want to make sure that you are safe". 

"I do like it. A lot. Thank you. Owe you one. And don't say it's your job". 

Kyuhyun was about to say something when his phone rang. Hyukjae called him to inform him that he managed to get all the fingerprints. And after comparing the fingerprints against some fingerprints found at the murder scenes, at the lost baggage storeroom at the airoort, and at the phone booth near Sungmin's condo, he zoomed down to 3 fingerprints. Mr Choi and the 2 contract staffs which the condo employed. 

Immediately after lunch, Kyuhyun drove to his office with Sungmin. He showed Sungmin the 2 men photo if Sungmin recognised them, or may had seen them around the condo since they were also contract security staff with the condo. Sungmin said yes, normally they were doing night shift and he would meet them if he reached home late at night. They were polite and didn't look suspicious. Kyuhyun said these 2 were also the ones who collected the lost baggages and were given the addresses to sent to. They were employed by a delivery courier company. The only problem is Kyuhyun's team still could not prove that they were the ones doing the killings. 

"Those addresses that they sent the baggages to, especially in those murder cases, were there any security cameras?" Sungmin asked. 

"Yes, and we have looked through those videos, the delivery guy wore a cap and looked down, we couldn't get a good picture of him" Hyukjae told him. 

"Is it ok if i take a look at the security cam? I might recognise them" Sungmin offered. 

"Hyuk, asked Henry to bring the videos. Those from the murder apartments and from their carparks".

"OK, sir" Hyukjae took out his phone. 

"Where's Hae? "

"He should be back soon from the police evidence static lab, after checking the handwriting" Hyuk started instructing Henry over the phone. 

"Sungmin, I go get some drinks for us. Caramel Latte with no sugar right?" Kyuhyun asked him. 

"Wow, you remembered! Yes thank you".

Henry came, said hi, and set up the monitor for Sungmin to view the videos. Hyukjae started showing him the first murder in Oakwood Asia condo in Gangnam-gu, pointed him to the guy with the strap-back cap, with the luggage. At one point when he was talking to the security desk, he did look up when the security man showed him the lift. 

"Stop the video" Sungmin told Hyukjae. "That's Seungri. Yes he is one of the 2 temp security guard". 

"You sure Mr Lee?"

"I recognised his side view because when I drove pass the security guardhouse, he would acknowledged me and turned back to his monitor to open the gate".

"Great. Do you know his full name?" and when Sungmin shake his head, Hyukjae said "ok we will check with the condo management. Let's see the 2nd crime scene. This is at The Hill. The luggage delivery guy wore a red cap. I guess that he roughly knew where were the cameras, so he avoided looking at the them". 

"Hmmm, this is difficult but the way he walked, he had a slight limp. The other temp security staff also has a slight limp. His name is Daesung, but yeah I cannot say 100% sure that this guy is Daesung, except for his limp leg".

"Heyyy found anything? " Kyuhyun walked in with 5 drinks. 

" Thanks, boss" Henry took his machiato latte, while Hyukjae thanked Kyuhyun too and took his coffee. Kyuhyun took Sungmin's caramel latte and pass to him. 

"Thank you. Hmmm smells nice" Sungmin smile at Kyuhyun. 

"You are welcome" Kyuhyun took his coffee and sip it. He put aside Donghae's coffee so that they don't accidentally spill it. 

"Sir, Mr Lee recognised the delivery guy in the first scene. And yes, he was one of the temp security guard" Hyukjae informed Kyuhyun which made him pulled a chair and sit next to Sungmin. 

"Wait, sorry Henry-ssi, can you rewind backwards about 5 seconds?  Once he walked to the elevator, he used his phone to make a call".

"What are you trying to get at, Sungmin? " Kyuhyun leaned forward. 

"It was the same as the 1st scene, Seungri called someone while walking to the lift, after talking with the reception. Do you have the video after the 2 guys went into the lift? The same footage? I just want to see whether another person walked in or not".

"Sure, hold on" Henry loaded back the first video. 

"Sungmin, what are you getting at? "

"Both guys did not carry anything except the luggage, so how can they hide a weapon or carry my book? There must be a 2nd person". 

"We thought about that too, Mr Lee, but the next few people are probably visitors, but maybe you are right, you might recognise one or two " Hyukjae started forwarding the 1st video until the part where Seungri was talking to the Security desk. After Seungri had call someone, he stepped into the elevator. They continue watching the video and about 3 minutes later, a guy walked in and showed something to the security and then went to the list too. 

"That's Mr Choi! Mr Choi Seung-hyun. I recognise his walking style, and he carried a haversack". 

"Oh Sungmin, we should asked you earlier. Ok, Henry, load the 2nd video again, and Hyuk, you forward to the delivery guy talking to the reception desk" Kyuhyun said. 

Sungmin confirmed that the next guy who walked in was Mr Choi. And on the 3rd and 4th scenes, the sane thing happened, the delivery guy would call someone after getting clearance to go up the lift from the security desk. 

They got their evidence. 

"Hyuk, we need to check Mr Choi's haversack. Get a warrant also to check his house".

"Ok sir"

"Sir! We got the match for the handwriting!" Donghae walked in from outside and when he saw Sungmin, "Ohhh, hi Mr Lee". 

"Hi Donghae-ssi"

"Good job Hae, tell me"

"The handwriting match with Mr Choi Seung-hyun. The condo security guard! "

"Really? He was the one who send me that letter? Why did he do that?" Sungmin was feeling very sad by now. 

"But sir, something is strange though.. " Donghae was feeling unsure. 

"What is it Hae?"

"The postage stamp. It was from a letterbox near your house. Meaning, the culprit stayed near your house!" Donghae looked up at Kyuhyun.