Police have arrested four teenage boys in connection with more than a dozen Edina High School students attacking a teenager in the city's YMCA last month and leaving him with brain injuries.

The assault occurred about 6 p.m. on Dec. 20 on the basketball court at the Y in the 7300 block of York Avenue, police said.

Police said the 16-year-old victim showed signs of a declining mental state and memory difficulties.

A 16-year-old boy was arrested Wednesday in Edina, police said, and three more boys were arrested Thursday: a 17-year-old and a 14-year-old in Edina, and a 16-year-old in Bloomington.

Charged so far as of midday Friday is one teenager who was 15 at the time of the incident, the Hennepin County Attorney's Office said. Because of the boy's age, prosecutors cannot release more information about him, what counts were filed or what the charges allege.

Potential charges of riot and assault are pending as of Friday morning. Police did not disclose the suspects' identities or a motive for the attack. Nor have they released the victim's identity.

Police said 13 boys who attend the high school were allowed to sneak in through the back door. Once inside, the group gathered in the gym and assaulted the targeted teenager, according to police.

The investigation is continuing, and police say that anyone with information about the incident should contact Detective Kenna Dick at 952-826-0491.