A St. Joe’s Prep grad is recovering from a traumatic brain injury after violent high school ‘tiki party’ in Wissahickon park

As graduating seniors at St. Joseph’s Preparatory School prepared for college, summer jobs, and other hallmarks of young adulthood this spring, 17-year-old Shawn Rinnier was focused on a simpler goal.

He hoped to muster the physical strength to walk across the graduation stage to collect his diploma.

That’s because the Bryn Mawr teenager is recovering from a traumatic brain injury that his parents say he suffered during an assault at a late-night party in Wissahickon Valley Park last month.

The attack knocked him unconscious, they said, and he has since experienced poor memory, fatigue, delayed vision, balance issues, and numbness in the right side of his body.

Now, in addition to caring for their son during what they expect to be a lengthy recovery, the Rinniers are seeking accountability for the people who assaulted their son.

“Nobody will talk at this point, and it just seems like people are trying to protect themselves, protect their friends,” said his mother, Susan Rinnier. “There’s some young adults that have a lot on the line here.”

Alongside investigators with the Philadelphia Police Department, Rinnier’s parents are working to piece together the events of the May 10 “tiki party” in the woods near Chestnut Hill, where they say about 250 teenagers had gathered before the evening turned physical.

Rinnier’s brain injury has left him with little recollection of what happened, said his father, Shawn Rinnier Sr., leaving his parents to look for clues after being sent photos and videos of the assault that partygoers took on their cell phones.

That night, students from a nearby Philadelphia private school as well as those from schools in the suburbs gathered for the party, which had been promoted on social media, Shawn Rinnier Sr. said.

He did not name the schools, deferring comment on those details to investigators.

The videos, Susan Rinnier said, show young people growing increasingly aggressive and eventually fighting.

“A couple fights broke out where the video evidence is showing that the other students were the aggressors” in the assault of her son, Susan Rinnier said.

“Some kids are on the sidelines yelling and chanting ‘punch on him’ and riling things up,” she said. “Our son, kind of scared, turns around and starts walking out of the event. The group follows him for about a second or so. That’s all we can see.”

A woman driving home in Chestnut Hill that night discovered Rinnier lying in the street around midnight and called 911, his father said. Shawn Rinnier Sr. later spoke to the woman, who told him “hundreds” of people had been fleeing through the woods with flashlights.

The parents did not recognize the young people involved in the assault, and they continue to communicate with detectives who told them they are interviewing people who may be involved.

A spokesperson for the police department did not return requests for comment on the investigation.

Rinnier was rushed to Jefferson Einstein Philadelphia Hospital and put on a ventilator, his parents said, and doctors later determined that his traumatic brain injury was moderate to severe.

“When he finally awoke, he was suffering from poor memory, couldn’t follow instructions, was confused, acting impulsive,” his mother said. The teen then moved to a rehabilitation unit at Bryn Mawr Hospital, where he continues to recover, she said.

The violent events of that spring night were life-altering, Rinnier’s parents said.

Their son, a tennis player, was preparing to attend the University of Florida on a scholarship this fall, they said. Those plans are now on hold.

Instead, the teen is taking part in an extensive outpatient rehab program, and his parents are working to have his enrollment deferred to 2027, when they hope he will be well enough to attend school.

Making sure that Rinnier took part in graduation at St. Joe’s last month was a more readily attainable goal, his parents said, and they were determined that he would achieve it.

Susan Rinnier was pleased to see that he was able to walk across the stage on May 31, even if he soon grew fatigued and experienced numbness in his legs after the ceremony, she said.

The Rinniers’ next hope is that police will find and charge their son’s attackers. Meanwhile, they continue to scan social media for additional photos and videos that may offer a better view of the incident.

“We owe it to Shawn to continue to move this forward any possible way we can, to get to the bottom of this,” his father said. “That’s our job as parents, and we’re not gonna stop.”