Another spokesman for the Police Department, Sgt. Robert Gomez, said at the news conference: “It is illegal to walk on a highway. It’s next to impossible for motorists to move out of the way of pedestrians on the roadway and that’s why it’s a restricted passage.”
On social media, some blamed the walkout for Jonathan’s death and called for schools to stop endorsing the protests, but Mr. De La Torre said the students who left the campus were an “isolated group.”
School walkouts took place throughout the country on Friday, the 19th anniversary of the Columbine shooting. It marked the third nationally coordinated gun control protest this year — each led by students, some of whom have had to participate in school lockdown drills since kindergarten.
They banded together to call for tougher gun laws, share firsthand stories about the violence that has roiled their communities and honor the 17 people who were shot to death in February at Marjory Stoneman Douglas High School in Parkland, Fla.
Jonathan’s mother, Ashley Benko, is a nurse in the University Medical Center’s emergency department, a spokesman for the hospital said, and his uncle, Michael Benko, works as a respiratory therapist there.
“All of us at U.M.C. are heartbroken by the loss of a child belonging to one of our associates, especially a child as young as Jonathan,” Jacob Cintron, the chief executive of the medical center, said in a statement.
The middle school had placed additional supervision at the back and front of the school, but the group of students left the school grounds on the east side, Mr. De La Torres said.
The school’s safety and security “is unparalleled,” he said, but when students choose to leave campus “it becomes more and more difficult to guarantee their safety.”
Jonathan’s death was a tragic accident, he said.
“What we’ve come to understand is that there are students out there that are very vocal, that are going to be our future leaders that are going to insist upon walking out,” he said. “And what we try to do is help them understand that they can still have a voice and that they can still have a presence and demonstrate their recognition and honor of some of the things that have happened in this country without leaving the premises.”
An earlier version of this article described incorrectly the victims of a school shooting in Parkland, Fla. Seventeen people died, but not all were students.