EVERETT — An Everett teenager allegedly admitted he shot another boy three times because he thought the boy was in a rival gang.

Sylius St. Amie, 16, also told police he was angry because he and his girlfriend had been fighting.

Prosecutors on Wednesday charged St. Amie with two counts of first-degree assault. He is charged as an adult because of the serious nature of the crime. St. Amie turns 17 next week.

Snohomish County deputy prosecutor Craig Matheson said that St. Amie is an extreme risk to the community and asked that the boy be held on $1 million bail. The violence Sept. 3 was unprovoked and the defendant admitted that he’s in a gang, Matheson wrote.

His gangs ties are “directly responsible for the motive to shoot” the victims, the deputy prosecutor added.

The victim, 17, isn’t in a gang. He and his sister, 14, were walking to Discovery Elementary School, where they planned to practice dance steps for the girl’s upcoming quinceanera, a traditional celebration to mark a girl’s 15th birthday.

They and a friend were on the path between the elementary school and Voyager Middle School when they encountered St. Amie and three girls. Witnesses say St. Amie, dressed in red, asked the other boy if he was “repping blue.” In other words, the defendant wanted to know if the other boy, who was wearing blue shorts, was part of a rival gang.

Some witnesses said the boy didn’t answer. Others remembered him saying, “no.” Whatever his response, St. Amie became enraged, Matheson wrote. He opened fire, striking the teen three times. The boy received through-and-through wounds to his left arm and right shoulder. He also was hit in the chest.

His sister rushed to his side and St. Amie allegedly shot the girl in the leg. St. Amie and his friends ran away.

A school employee came to the boy’s aid and tried to stem the bleeding from the chest wound. The victims were taken to Harborview Medical Center in Seattle.

Investigators found four shell casings at the scene.

Police received tips about the identities of the shooter and the three girls. Officers interviewed the girls, who corroborated that the shootings were unprovoked. They told police that St. Amie routinely carries a gun and they know he is associated with a gang.

They eventually told police that St. Amie was hiding in a house on 115th Street SW. A SWAT team attempted to get the teen to surrender. He refused and several hours later tear gas was fired into the house. Deputies found him lying on a shelf in a closet.

The also found a .22-caliber handgun in the house. The gun was reported stolen May 11.

St. Amie is expected to be arraigned Friday. He doesn’t have any prior felony convictions.

Gang crimes are on the increase in Snohomish County. The day of the shooting another suspected gang member was in a Snohomish County Superior Court answering to allegations that he shot a 15-year-old boy last month in south Everett.

Juan Beteran Monrroy pleaded not guilty to first-degree assault and drive-by shooting. He was being held on $500,000 bail.

Prosecutors allege that Beteran Monrroy, 18, opened fire on a pickup truck using a military-style assault rifle. His targets are believed to be connected to a rival gang.

The victim was struck in the armpit. The bullet perforated his heart but the teen is expected to recover, Snohomish County deputy prosecutor Bob Langbehn wrote.

Police were told that on Aug. 16 the boy and three other gang members were riding around looking for Beteran Monrroy with the intent to beat him up. They were stopped at a light and noticed him beside them in a Honda.

Beteran Monrroy allegedly placed the rifle on top of his car and pointed it at the victims. They threw a metal bat and a knife at him and then sped away. He gave chase and allegedly fired several rounds at the pickup truck.

Deputies found bullet holes in the pickup’s tailgate, back window and backseat.

Monrroy was arrested at a nearby apartment complex. They found a rifle in the car. Police also found a revolver under the front passenger seat.

Diana Hefley: 425-339-3463; hefley@heraldnet.com. Twitter: @dianahefley.