In Police University, episode 13, Sun-ho took heavy risks in order to find the top man behind the online gambling ring. He wanted to ensure that neither he nor his mentor Dong-man would be in further danger.
The investigation into the gambling ring got extremely dangerous when Dong-man had met with an accident. It was a planned attack and this was proved when the Police Commissioner said as much in the hospital.
He had also warned Dong-man not to get involved any further as they would target Sun-ho next. Kang-hee overheard the entire conversation and that is why she decided to stop Sun-ho in Police University, episode 13.
Why did Kang-hee betray Sun-ho and his friends in Police University, episode 13?
Kang-hee believed that the further Sun-ho investigated the case, the more danger he would be in. So not only did she stop helping him, she actively stood in his way. Sun-ho had received a hint about the man that he was after in Police University, episode 13.
He received a keycard from one of the hackers who had worked with Mr. Go and was told that there was a safe within the university. This safe held all the secrets and Sun-ho had to find out where exactly the safe was kept.
In this attempt, his other friends Bum-Tae and Joon-wook tried to help him. However, Kang-hee had used Min-kyu to stop the two of them from going any further than the armory. This was the only place on campus that was kept under lock and key even from students.
That was the first place that the two of them checked before they got caught by the student patrol officers. They did, however, give Sun-ho the much-needed clue in Police University, episode 13. The night after his friends got caught, Sun-ho tried to enter the armory and succeeded. He also hacked into the safe.
Where did Sun-ho find evidence against Hee-soo in Police University, episode 13?
Sun-ho opened the safe to find a bunch of documents. Just when he thought he would finally know the truth behind the gambling organization, the hacker who tipped him off double crossed him and pulled a gun on him as well.
It was Kang-hee who appeared at the last moment to help Sun-ho. From the beginning in Police University, episode 13, her plan was always about stopping Sun-ho from getting hurt. While her actions may have seemed problematic, she turned up to help her boyfriend just when he had needed it.
One of the documents in the safe was a picture of Hee-soo with Chul-jin and other kids and adults. This was taken for some foundation that all of them belonged to. However, the logo of the foundation was similar to the logo of the gambling ring and that is why, Sun-ho is suspicious of Hee-soo in Police University, episode 13.