On a sunlit day in June, Cara Lynn Golias joined a group of friends at their secret swimming hole in Hemlock Overlook Regional Park, splashing into the water from a rope swing tied to a railroad trestle.

Cara and her friends, who called themselves the “Naughty Nine,” relaxed beneath the bridge over Virginia’s Bull Run, smiling for a group photo with their toes in the silty shallows.

It was “perfect,” she later tweeted, and by all accounts a carefree afternoon for a 16-year-old with a bright future. Cara, a star cross-country runner, had earned the grand prize at a regional science fair for her microbiology research on E. coli, and she made all A’s as a Fairfax High School junior, her father said.

But on Sept. 28, for reasons still unknown to her family, Cara returned to the place she treasured most, slipping into the woods near Manassas Park and hanging herself from the railroad bridge.

“It took everybody by surprise,” said her father, Michael Golias. “That’s why we’re still trying to figure out what happened.”

Cara Lynn Golias at the top of Angel's Landing at Zion National Park. (Courtesy of family)

Cara was one of three teenage girls from Fairfax County who died in apparent suicides since September, including a 17-year-old South Lakes High senior and a 15-year-old Robinson Secondary sophomore, schools officials said.

It’s an alarming number of female teen suicides for a county that had 13 suicides among girls between the ages of 10 to 19 from 2003 to 2013, according to Virginia Health Department figures, an average of just more than one a year. The three deaths come as the school system has begun to overhaul its teen mental-health policies since six suicides in three years at W.T. Woodson High School and two suicides within 24 hours last fall at Langley High School.

Experts with the federal Centers for Disease Control and Prevention and the Fairfax County Health Department are now investigating potential suicide clusters in the county at the request of state health officials. This week, CDC experts have led focus-group meetings with parents at eight high schools, including Fairfax, Langley, Robinson, South Lakes and Woodson, to identify risk factors and suicide-prevention strategies, according to a schools document.

Glen Barbour, a spokesman for Fairfax’s Health Department, said that the CDC experts will “help investigate the risk factors that may be contributing to youth suicides in Fairfax County and to make recommendations on what additional prevention steps could be taken.”

Kim Dockery, the county’s chief academic officer, said the school system has received multiple grants to focus on students’ mental health, including $50,000 in federal aid targeted for Woodson High. Another grant from the state will allow the school system to spend $2.8 million over the next five years on expanding a mental-health first-aid program.

To help identify teens in distress, Dockery said, all middle school and high school teachers are enrolled in mental-health awareness training this semester. A new county suicide help line that lets teens send text messages has proven life-saving, Dockery said.

“Suicide is a very complex issue,” said Asha Ivey-Stephenson, a behavioral scientist with the CDC in Atlanta. “It’s something that is preventable, and it’s a public health problem.”

Ivey-Stephenson said that although females are more likely to have suicidal thoughts, males are more likely to go through with suicide. She said the suicide rate among males tends to be four times that of females across all age groups.

According to data from the Virginia Department of Health, suicide is one of the top causes of death for those between 10 and 24 years old.

Marc Leslie, who oversees the state’s Violent Death Reporting System, said that between 2003 and 2013, males ages 10 to 19 had a suicide rate of 5.5 per 100,000. During that same span, females ages 10 to 19 had a suicide rate of 1.8. He said that each case is multifaceted, which makes investigating the root causes of suicides particularly frustrating for data scientists and families.

“It’s often a mystery,” Leslie said.

Golias said his daughter’s death shocked her family members and left them with questions that might never be answered.

“It’s like, ‘Cara, why did you do this? You were loved. You had a great heart.’ This is the question we all have,” her father said. “Her future looked so bright. . . . She was intelligent. She had great friends. She was part of the church group. She had loving parents and a loving family. She was involved with team sports. She was well-liked. But nothing that we saw could have led to something like this.”

Cara was a soccer player and long-distance runner; she ran the Marine Corps Marathon at age 14 in 2011, one of three times she completed the race with her father.

Last month, Golias ran the marathon again, a race he had planned to take part in with his daughter. Instead, he pinned Cara’s bib on his back and ran in her memory. Approaching the finish, he turned and ran backward so that Cara crossed the line two seconds ahead of his official time. The Marines handed Golias a finisher’s medal for himself and a second to keep for Cara.

“You wouldn’t want to wish this on any other parent, because kids are such a big part of your life,” Golias said. “I’m sad for the loss of memories I would have made with Cara . . . and also I’m sad that Cara will not be able to experience some of the pleasures of this life. Graduating high school. Graduating college. Her first job. Getting married. Having a honeymoon. Having a child of her own. Celebrating her child’s first birthday. . . . Those are the things I’m going to miss with Cara.”

Golias, who is divorced from Cara’s mother, encouraged parents to do whatever it takes to help their children if they are in distress. He said his daughter had been taking part in mental-health therapy in the months before she died. He also encouraged families to talk to other teens, who might see signs that parents miss. A memorial fund in Cara’s honor raised $16,166 for the American Foundation for Suicide Prevention.

“Do what you need to do to ensure that this doesn’t happen to your child,” Golias said. “Seek out professional help. Shower your child with love and understanding. Be there for your child.”

On Oct. 30, Cara’s birthday, her friends went back to their favorite swimming spot.

They created a memorial in her honor and left flowers beside a makeshift cross they planted in the rocky banks in the bridge’s shadow.