Said Ivanov just bought an AR-15 last week and close friends were worried

Friend of Ivanov told Daily Mail Online that he was depressed after his split with Bui, his girlfriend of more than a year

Alexis ran back inside the house and hid in a closet until police arrived

But as they began to run into the street the gunman fired shots from roof

A boy who was throwing the party tried to help her escape out the garage

She told her grandmother that she watched her friends get shot dead

Alexis Gemmer, 18, was one of the 20 young people at the party

Anna Bui, Jordan Ebner and Jake Long have been identified as the victims

Allen Ivanov, 19, was taken into custody following the mass shooting

It was supposed to be a regular summer night in a small town. A group of high school friends, recently graduated or back from college, reunited at a house party in their old stomping grounds.

But that peace was shattered just after midnight in Mukilteo, Washington, when 19-year-old Allen Ivanov allegedly walked into a party full of his friends, including his ex-girlfriend, and opened fire.

Alexis Gemmer, 18, was one of the 20 people. She saw her friends get shot.

Anna Bui, Jake Long and Jordan Ebner were all killed. Bui was Ivanov's ex-girlfriend.

Scroll drown for video

Mukilteo police have confirmed to Daily Mail Online that Allen Ivanov is in custody following a mass shooting in the affluent Seattle neighborhood of Mukilteo that cost the lives of three young people on Saturday morning

Anna Bui has been confirmed as one of the three victims. She and Ivanov reportedly broke up last week

Jordan Ebner, a student at Everett Community College, also lost his life in the horrific mass shooting

Jake Long (pictured with his girlfriend at prom) was the third victim of the tragedy that has rocked Mukilteo

Will Kramer, 18, (pictured left) was injured during the shooting. He is currently in serious condition

Alexis hid in a closet until police arrived at the home in the waterfront Chennault Beach neighborhood, called her grandmother and told her the horrifying things she had just seen.

'She kept saying, "They're dead, they're dead, I was right there and I saw them"', Susan Gemmer told the Seattle Times.

Alexis told Gemmer that the gunman arrived at the party, filled with recent graduates of Kamiak High School, with a rifle and immediately went to the back of the house.

He shot two people at the fire pit in the backyard before going onto the roof, where others were hanging out, and opened fire.

After the first shots rang out, the young man who lived at the home tried to help Alexis escape the house safely and led her out the garage.

They rolled under the garage door but as the teen tried to run across the street, the gunman began to shoot at him from above on the roof.

Alexis panicked and went back into the home, barricading herself in a closet. The young man was able to make it across the street.

Another teen, 18-year-old Will Kramer, was injured during the attack. He is listed in serious condition at Harborview Medical Center in Seattle.

Ivanov, an incoming sophomore at the University of Washington Bothell campus, is being held for investigation of three counts of murder.

Alexis Gemmer, 18, (pictured) was one of the guests at the party. She called her grandmother as she hid in a closet, saying she had watched her friends get shot dead

The house party was taking place at this $1million residence in the waterfront Chennault Beach neighborhood, about 25 miles north of Seattle

Ivanov posted a picture of this rifle, with three bullets on the side, on his Instagram account just days before the shooting. The rifle has a sticker from exclusive New York streetwear brand Supreme

Ivanov, a University of Washington student, also posted a cryptic tweet on Thursday

Ivanov also posted this tweet, which seems to be a reference to Ruger Firearms. A friend commented on the tweet in the early hours of Saturday morning after the shooting

He was arrested over 100 miles away in Lewis County when officers spotted a car that matched the suspect's description about two hours after the shooting.

Officer Myron Travis told Daily Mail Online on Saturday that police are not looking for any other suspects.

The shooting has rocked the tiny affluent town of Mukilteo, where students often walk at graduation with the very same people they began kindergarten with.

Hundreds of teenagers gathered at Kamiak High School on Saturday night to pay tribute to their fallen friends - and express shock at the classmate who allegedly murdered them.

'Allen was very calm, very handsome, ladies loved him,' a close friend of Ivanov's, who asked to only be identified as a Baltimore college student, exclusively told Daily Mail Online.

'He was a very friendly guy, very smart.'

On the outside, it appeared Ivanov had it all. He was a computer science and engineering major who worked at the Genius Bar at Apple.

Authorities said the suspect fled the $1million home in a 2016 Subaru WRX. Ivanov had recently posted multiple pictures of a Subaru WRX (pictured) on his Instagram

Ivanov's LinkedIn page said he is an engineer and founder at Skirmos, an open source laser tag system

The 'Skirmos experiences' (pictured) allows users to experience their 'favorite video shooter game in real life'

He is also listed as an engineer and founder of Skirmos, an open source laser tag system that allows users to 'imagine your favorite first-person video game in real life'.

A Kickstarter campaign raised more than $90,000 for the factory prototypes.

His Instagram portrayed the life of a young man on the cusp of success. He posted multiple pictures of his brand new Subaru WRX, the same car he allegedly fled the shooting in.

Classmates said Ivanov was known for his intelligence and that the community was proud of his success.

'I expected him to be the next Bill Gates,' Jansen Garside told the Seattle Times.

'There's not a shred of me that thought he was capable of this.'

But those who were close to Ivanov said he had become depressed and distraught after his split with Bui, which some say occurred a month ago while others believed it only happened last week.

The Baltimore college student told Daily Mail Online that Ivanov purchased an AR-15 rifle last week.

Just two days before the shooting, he posted a picture of the gun on Instagram, with three bullets by the weapon's side.

The rifle was personalized with a sticker from the exclusive Supreme New York streetwear brand that reads: 'Supreme 16 You Still Suck'.

Hundreds of students gathered at Kamiak High School on Saturday night to pay tribute to the three victims

Devastated students could been seen crying in disbelief as they remembered their former classmates

Kamiak residents said Jordan, Jake and Anna were well-liked, and all friends with each other

A piece of blue painter's tape on the gun can also be seen. It reads 'Christopher', Ivanov's middle name.

The caption of the post reads: 'You can't run with me.'

Ivanov also posted cryptic tweets on his Twitter two days before the shooting.

'First and last tweet,' he wrote on July 28. 'I've been through it all.'

He then tweeted 'What's Ruger gonna think?', which seems to be a reference to Ruger Firearms.

Several friends became so concerned that they reached out to Ivanov's parents and asked them to return the gun, but they didn't believe Allen could ever do something so horrific.

And, the friend, added, neither did anyone else.

'I don't think his parents knew he was capable of something like this,' the friend said. 'We didn't know he was capable of something like this.'

The friend in Baltimore, who first met Ivanov two years ago through playing Halo online, said he called at 2.30am on Saturday.

Bui has been described as the 'sweetest girl' with the 'kindest and happiest' soul by her former classmates

She was voted Most Talented by her senior class and was extremely involved in her school. Pictured is a collage one friend made to show how many extracurricular activities Bui participated in

Jordan (left in the black suit) was a student at Everett Community College. Jake (right) is being remembered by friends as a great baseball player

'Throughout the phone conversation he kept asking "What's the best way to kill myself?", he was crying, saying "What did I just do?'"

The friend tried to convince Ivanov to park the car, and immediately called Seattle Police. But it was too late.

'He was definitely in an altered state of mind,' he said. 'The Allen that I knew was not anymore, that was definitely not Allen that I was talking to.'

Devastated friends are now left only with the memories of Anna, Jake, and Jordan, paying tribute to their talent and smiles that could light up any room.

Bui was voted 'Most Talented' by her senior class. Friends said she dreamed one day of being a nurse.

A Kamiak graduate, who did not want to be identified, told Daily Mail Online that she had a class with Bui, who she described as the ‘sweetest girl’.

‘She always had a smile on her face and a joke at the ready,’ she said.

‘She had so much energy and a light about her that could just brighten up a room. If she was in the building, you could hear her laughter.’

‘She cared so much about her friends and was so full of love. She had a huge heart.’

Kayla, a senior at Kamiak, said Anna had been her idol both in choir and life itself.

'She was the kindest and happiest soul,' Kayla told the Daily Mail Online.

Members of Kamiak Choir organized a candlelight vigil at the high school on Saturday night to honor Anna, Jake and Jordan.

Garside said Long, who friends remembered for his talent in baseball, was 'completely selfless'.

Ebner also played baseball and was attending Everett Community College. He worked at an auto-detailing shop during and after high school.

'He's the guy that always has a smile on his face,' Jase Wiley told KGW. 'Super sweet, just happy.'

Purple ribbons were tied to trees and that the flag was lowered to half-staff in front of Mukilteo City Hall.

Even the local McDonald's had a message: 'Mukilteo Strong'.

Parents could be seen waiting outside in the early hours of the small community as they waited to hear more information about their children