A fourth student passed away Wednesday morning after the deadly school shooting in Oxford Township, Michigan, Tuesday afternoon. The deadly shooting had already claimed the lives of three others and injured six students and one teacher. Those who were injured range in ages from 14 to 17. A 47-year-old teacher was also injured but was discharged Tuesday evening. At least two of the students who were shot are still in critical condition.

The 15-year-old sophomore who was identified as the shooter was taken into custody shortly after the first phone call to police came in. Authorities shared Tuesday evening that after the boy spoke with his parents, he was advised not to speak to officers and instead follow the advice of his lawyer.

In a press conference Wednesday morning, Sheriff Michael Bouchard shared new details in their investigation. Bouchard explains that authorities were combing over hours of school security footage in an attempt to track the 15-year-old’s movements leading up to the attack. Bouchard explains that the boy went into a bathroom before he emerged with a 9 mm Sig Sauer handgun. The teen then began to shoot at classmates in the hallway, at times shooting into classrooms. It's not yet clear what the boy’s motive was, but Bouchard shares that his victims “appear random.”

The sophomore shot roughly fifteen to twenty shots with the semi-automatic handgun before he surrendered himself to an officer that was stationed in the school.

During the press conference, Sheriff Bouchard explained that he wanted the sophomore to be charged as an adult. However, he adds that the decision would be left up to the prosecutor's office.

On Wednesday evening, the prosecutor’s office announced that they would be moving forward with charging the teen as an adult. The teen faces four counts of first-degree murder, one count of terrorism, seven counts of assault with intent to murder, and 12 counts of possession of a firearm in the commission of a felony.

In an interview on CNN, Sheriff Bouchard later explained that the suspect had the intention to kill his targets. “​​He was shooting people at close range, oftentimes toward the head or chest. It’s chilling. It’s just absolutely cold-hearted murderous.”

Wednesday morning, footage captured by students inside a classroom reveals just how menacing the 15-year-old sophomore was. The footage shows students huddled together inside of a classroom with one person inside the room talking to the suspected gunman outside of the classroom.

“Sheriff's office. It’s safe to come out” a voice outside of the classroom can be heard telling the students inside. A male voice inside the classroom responds, "We're not willing to take that risk right now." The voice outside the room then replies, “Ok, well, open the door and look at my badge, bro." A student inside the class can be heard saying, “He said ‘bro’ red flag.” Pandemonium erupts as students begin escaping the classroom through a window on the opposite end of the room. The students then run across what appears to be a courtyard until they reach a door where a sheriff's deputy helps pull the students into the building again.

The victims in the shooting have been identified as Hana St. Juliana, 14, Madisyn Baldwin, 17, and Tate Myre, 16. Myre passed away in the back of a sheriff's vehicle on his way to the hospital. On Wednesday morning, 17-year-old Justin Schilling succumbed to his injuries and was identified as the 4th victim. The shooting has been classified as the deadliest shooting on school property this year.

While it's unclear what the motive behind the 15-year-old’s shooting rampage was, authorities have been able to identify where he got the gun. Officials say that the gun was purchased just four days earlier by the suspect’s stepfather. In an earlier press conference, authorities shared that when the sophomore was apprehended, there were still seven live rounds in the gun.

Following the shooting, reports began to circulate that some students knew about a possible threat against the high school. The reports appear to be related to a letter that was sent to parents by the school’s administration on November 12.

The letter explains, “We are aware of the numerous rumors that have been circulating throughout our building this week. We understand that has created some concern for students and parents.” The letter adds, “Please know that we have reviewed every concern shared with us and investigated all information provided. Some rumors have evolved from an incident last week, while others do not appear to have any connection. Student interpretations of social media posts and false information have exacerbated the overall concern.” The administration goes on to add, “We want our parents and students to know there has been no threat to our building nor our students.”

One parent, Robin Redding, shared with the Associated Press that her son Treshan Bryant had opted not to go to school the day the shooting happened. Redding explained that her son had a ‘bad feeling’ about attending school because of his perceived threat of potential violence.

Local reports also indicate that the parents of the shooter met with school administration the day before and the day of the school shooting. Officials have yet to provide information on what those meetings were about.

Despite potential threats against the school, authorities maintain that there was no indication an event as tragic as a school shooting could occur. “There was no prior information shared with the Sheriff’s Office or the School Resource Officer before the incident,” Sheriff Bouchard explained.