Homicide

Murder is a bloody way to eliminate your rival or chosen student.

In order to murder, you need a weapon. With a weapon equipped, you can attack a nearby student. If you attack a student, they will shout "What are you-" and scream loudly before collapsing to the ground in a pool of blood. Your uniform will have several splatters of blood on it, and your sanity will have been decreased. The more students you murder, the more blood there will on your uniform, and the more sanity you will lose. The student(s) you've murdered will not return to school the next day unless you restart the week.

You can attack a teacher, but won't be able to successfully murder her as she will overpower Yandere-chan. You will have to allocate enough study points during class into the Physical Education stat to get to rank (?) to attack/counterattack teachers, which has not been implemented yet. Trying to attack a teacher will result in being expelled. If a teacher witnesses you murdering a student, or has realized that you are the murderer, she will chase you down and pin you to the floor. You cannot outrun a teacher as they have a faster run speed.

As of the September 1st update, students will scream loudly if they are murdered. The students in the scream's range will turn around and scream as well. This lowers the School Atmosphere. The only way to murder students without being caught at the atmosphere's lowest point is to do it in a secluded area, like a bathroom, or far away from the other students.

In future updates, as your sanity drops, killing animations will take longer and after a student witnesses two murders, they will flee immediately. At low school atmosphere, students might take out their cameras and take a picture of you immediately after they witnessed the murder, which could lead to an instant game-over.[1]

Witnesses
When a student witnesses Yandere-chan murder another student, the witness may react in several different ways depending on their persona. So far, only two personas have been implemented into the game—Coward and Teacher's Pet.

Coward
If a student with the persona of a coward witnesses murder or sees a corpse, they will flee the school and call the police, giving the player a total of 5 minutes to dispose of the corpse, blood, and any evidence. If Yandere-chan manages to do so, (or at least get rid of the clothes, the weapon, and pictures on the phone) the police will not be able to uncover any evidence that a murder had taken place on school grounds, and Yandere-chan will not be arrested.

Teacher's Pet
If a student with the persona of a teacher's pet witnesses a murder or sees a corpse, they will run to their favorite teacher and inform them of what they have seen. The teacher will request the student to lead her to the corpse. If Yandere-chan has cleaned up the crime scene before the teacher arrives, the teacher will accuse the student of pranking her, and will then return to her classroom. This will leave the witness mentally scarred for the rest of the game. The student will try to convince the other NPCs that Yandere-chan committed murder, impacting your reputation negatively. If more than one student with the Teacher's Pet persona witnesses murder, every one of them except the first witness will hide in their classroom instead of informing a teacher.

Hero
This has not been implemented yet. If a student with a Hero persona witnesses a murder, they will try to apprehend you. If you fail to get out of their grasp, a Game Over will appear.

Evil
This has not been implemented yet. If a student with a Evil persona witnesses a murder, they will congratulate you on your kill and swear silence about this event.

Fragile
This has not been implemented yet. If a student with a Fragile persona witnesses a murder, they will beg you to not kill them. You can choose to let them live or die.

Cleaning Up After a Murder
The first thing the player should do is dispose of the corpse. Grab the corpse by one of their four limbs and walk to the incinerator which is located to the left of the school gate.

Running while dragging a corpse without having allocated enough study points into the Physical Education stat to get to rank 2 during class will cause you to stop dragging the body.

Dump the body into the incinerator, dispose of the murder weapon, dispose of the bloody uniform (the clean uniforms are located in the Shower Room), fill the water bucket with water from the sink, and mop up the blood (the mop, sink and water bucket is currently located to the left of the incinerator). Stepping into pools of blood can leave bloody footprints that you have to clean up too. You can use Yandere Vision to find any blood you may have missed. Dragging a body also creates more pools of blood as it bleeds out. If the mop is too saturated with blood and turns bright red, dip it in the water bucket. The water will get bloody as you dip the mop in. If the water gets too bloody, empty it in the sink and fill it up again.

At this point, the player should activate the incinerator, erasing all of the evidence. In the August 12th update, you can obtain a new clean uniform in the shower room. Once you incinerate a weapon, they will respawn the next day.

Failure to Clean Up
If Yandere-chan fails to complete all of the tasks necessary to get away with murder, then one of following reactions will occur, ending the day.

Witnessed by a student
Coward Persona: If a student with the Coward persona witnesses you committing murder, and you fail to clean up during the given amount of time, Yandere-chan will be taken into custody by the police, and if there is evidence of Yandere-chan being the murderer, she'll be arrested. If the murder can't be linked to Yandere-chan, she won't be arrested, but she'll have a nightmare that night about losing Senpai.

Teacher's Pet Persona: If a student with the Teacher's Pet persona witnesses murder and you only dispose of the evidence of Yandere-chan being the murderer, the teacher will call the police and remain by the student's corpse, guarding it until the police arrives. The police will not be able to link Yandere-chan to the murder because of a lack of evidence. However, if you fail to dispose of evidence that Yandere-chan is the murderer (such as a bloody uniform or a murder weapon lying around), and the teacher sees Yandere-chan, the teacher will realize Yandere-chan killed the student and chase Yandere-chan, pinning her down, resulting in a game over. If the police arrives and you've failed to dispose of all evidence that Yandere-chan is the murderer, the police will be able to link Yandere-chan to the crime, resulting in Yandere-chan being arrested.

Not witnessed by a student
If you're not witnessed by a student, a teacher will come across the corpse after the school day ends while walking through the school to tell any lingering students to leave. If you dispose of all other evidence and only leave the corpse and/or blood on school grounds, Yandere-chan will not be arrested. However, if you leave any evidence with it, the police will arrest Yandere-chan.

If blood pools, bloody weapon(s) or a bloody uniform gets witnessed by a teacher after the school day ends, she will question it, but not call the police.

Trivia
Yandere-chan holding several different weapons.
 * In the future it should be possible to murder people with your bare hands under very specific circumstances, but not by default.
 * If you murder everybody at school throughout the entire game, there will be a unique special ending (in the final game).
 * Murder is called "Homicide" in the Challenges.
 * An NPC will not report a murder if they hated the victim or have an 'evil' persona.
 * If you kill 4 Students, you will become visibly insane.
 * Murdered students' parents will notice their kid did not come home from school, which is why the School Atmosphere drops a little.

Quotes
5.    https://twitter.com/YandereDev/status/646038760916779008