GEOFF BENNETT: Violent crime is on a downward trend across the country since a pandemic era spike.

But, today, a number of cities are reporting a new rise in violent crime among youth.

In many cases, law enforcement says social media played a central role.

Stephanie Sy reports from Maricopa County, Arizona, about the challenges of addressing teen violence.

STEPHANIE SY: A little over a year ago, Connor Jarnagan's typical suburban teen life took a dark turn.

CONNOR JARNAGAN, Teenager: Until that moment, I did not think people had such an evil in their heart to do something like that to somebody.

STEPHANIE SY: While waiting in the parking lot of an In-N-Out, Connor said he was confronted by about a dozen teen boys.

The leader demanded $20 and Connor resisted.

CONNOR JARNAGAN: I worked for this money.

You are not going to just take it from me.

So, I said no until he punched me with brass knuckles.

The whole time, there was blood just gushing down my head.

I was shaking and crying, because I did not know what was going to happen to me.

I did not know if I was going to live.

It was really scary for me.

STEPHANIE SY: The suburb where it happened, outside Phoenix, is what his mom, Stephanie, described as a bubble, billing itself in recent years as one of the safest cities in America.

STEPHANIE JARNAGAN, Mother or Connor Jarnagan: We live in Gilbert, Arizona.

It is a bedroom community.

I never thought that that would happen to my son.

Letting him go have a burger with friends at dinnertime, like, I did not think that that would be unsafe.

STEPHANIE SY: It turns out the teen who assaulted Connor was part of a group who called itself The Gilbert Goons.

CONNOR JARNAGAN: There's videos of him fighting people all over the Internet.

STEPHANIE SY: The group members were known for posting videos of each other flashing guns, ganging up on teens, and street racing.

Examples of teen violence span social media and the country, from Missouri where a 15-year-old girl attacked another teen, landing her in the ICU, to Stockton, California, where a group of teens filmed the beating and robbing of an 8-year-old.

The violence by The Gilbert Goons, which, although recorded, went unchecked by law enforcement for the better part of a year, culminated in the death of 16-year-old Preston Lord last October.

While a group of attackers pummeled him, some teens called 911, while others stood by, recording on their phones.

CHUCK BONGIOVANNI, Gilbert, Arizona, Councilman: Why do you have 40 kids with a camera recording violence?

I saw a five-second video of Preston before they did CPR.

And I don't ever want to see a video like that again in Gilbert.

STEPHANIE SY: As community grief turned to outrage over the death of Lord, Gilbert town Councilmember Chuck Bongiovanni helped set up a subcommittee to address teen violence.

At a recent meeting, half the attendants were area high school students.

CHRISTINE NJUGUNA, Gilbert Mayor's Youth Advisory Committee: Just one thing I would say would be a big deal while going to these schools is just also teaching children accountability.

You will be accountable, not only with police and everything, but just like general morals.

STEPHANIE SY: While moral accountability is called for by some, many others are calling for stronger law enforcement and curfews.

CHUCK BONGIOVANNI: Now, with social media, it is creating personas these kids usually really wouldn't be if they did not have social media.

STEPHANIE SY: A 30-minute drive from Gilbert, Commander Gabe Lopez says the number of teens murdered in his city last year rose significantly from the year before, as did the number of teens charged with homicides.

Lopez is head of the Phoenix Police Department's Violent Crimes Bureau.

He points out the scene of a shooting late last year during a particularly violent stretch.

CMDR.

GABE LOPEZ, Phoenix Police Department: I think a total of nine victims are what these two individuals were charged with.

So, of the four people in the car, two were charged with the homicide.

STEPHANIE SY: And they were juveniles?

CMDR.

GABE LOPEZ: They were juveniles.

And, again, the victim was 15, the suspects were 17, and then you had a 10-year-old shot.

STEPHANIE SY: Federal statistics show, in 2020, homicides committed by juveniles were the highest they'd been in two decades.

CMDR.

GABE LOPEZ: The fear that I have, and I think it's shared by others in law enforcement, is people are doing or committing crimes so that they can capture it, so they can post it on their social media feed, so they can get street cred, or so that they can get likes.

JAMES GARBARINO, Psychologist: Youth culture has moved in the direction of celebrity is the number one value.

STEPHANIE SY: Psychologist James Garbarino has spent decades researching adolescent violent behavior.

JAMES GARBARINO: The cultural immersion in violent imagery is so powerful in the United States and, of course, social media, the rise of social media as a context in which those expressions can be offered, it's certainly it's not just limited to 2020 and onward, but it has escalated as well.

STEPHANIE SY: Commander Lopez says social media has also changed the landscape of gang violence.

CMDR.

GABE LOPEZ: Traditionally, it had always been really focused on the neighborhood that you were from, a group of friends that you typically grew up with.

Nowadays, they meet online, they communicate via social media.

It's a hybrid mix of different races, different areas of the city.

It's complicated as far as trying to police that.

STEPHANIE SY: Before Olga Lopez moved to the Phoenix suburbs from California two years ago, she made sure it was a safe town where her son Jeremiah could play on a competitive high school football team.

But, last may, Jeremiah was shot and killed at a fellow student's home in Mesa.

He was 18, weeks away from graduating high school.

OLGA LOPEZ, Mother of Shooting Victim: The teammate who lives in the house along with the young man that lives across the street, were pointing guns at Jeremiah multiple times and recording it and posting it to Snapchat.

STEPHANIE SY: In the video described to her, Lopez says the laser from the guns pointed at Jeremiah shone red dots on his face.

OLGA LOPEZ: One time, Jeremiah says: "Hey, chill."

Another time, Jeremiah is trying to make light of the situation.

A little under 30 minutes later, my son is fatally shot in the back of the head.

I vowed that I would show up with the same grit and determination that he did.

STEPHANIE SY: Olga got the devastating news on May 7.

OLGA LOPEZ: It isn't something that you get over.

It definitely isn't something that time heals.

And every day is like the first week.

STEPHANIE SY: She pours herself into running a nonprofit foundation she set up with her oldest son in Jeremiah's name.

While social media may have played a role in both Jeremiah's death and the attack on Connor Jarnagan in Gilbert, it was also what helped pin down the suspects in their cases.

Jarnagan helped lead police to his attacker.

CONNOR JARNAGAN: They got into his phone, and they looked at his chats and there it was: "I hit this guy and he gave me $20."

STEPHANIE SY: Connor says a lot of teens have been afraid to report on their peers, for fear of retaliation.

CONNOR JARNAGAN: Teens need to come forward and stop being in the shadows, stop recording these fights.

Instead, do something about it and make our communities a safer place.

STEPHANIE SY: He's doing his part by calling for Arizona state lawmakers to ban brass knuckles for minors.

That action is tabled for now.

CONNOR JARNAGAN: I'm hoping both sides of the aisle, Republicans and Democrats alike, can come together on this issue.

STEPHANIE SY: Connor continues to heal.

And part of that, he says, has meant forgiving the teen who attacked him.

For the "PBS NewsHour," I'm Stephanie Sy in Maricopa County, Arizona.