Neighbors said the display of hate in a Lorton, Va., community was as large as it was shocking: a swastika roughly 40 feet across mowed into the grass of a community field.

Tire marks from a riding mower ran from the lot and up a road to the home of a teen who was known as troubled in the neighborhood, leaving little mystery as to the perpetrator, a neighbor said. Residents of Gunston Manor were soon debating how to handle the situation: go to police or talk to the teen’s family directly?

The latter plan won out — and now some regret that decision.

The incident came roughly two months before the 17-year-old allegedly shot and killed the parents of his 16-year-old girlfriend in their Reston home Friday. Scott Fricker, 48, and Buckley Kuhn-Fricker, 43, had forbidden their daughter to see the teen after family and friends said the couple discovered a Twitter account they believed was linked to the teen. It retweeted tweets praising Hitler, made derogatory comments about Jews, called for "white revolution," and showed an image of a man hanging from a noose beneath a slur for gays, among other objectionable content.

The teen, who has been charged with two counts of murder, remains hospitalized in critical condition after turning the gun on himself.

Penny Potter, a neighbor, agreed to share the story of the swastika because she wanted it to serve as a cautionary tale to report early-warning signs before a tragedy occurs. She doesn’t know whether the Frickers would still be alive if neighbors had contacted police, but she believes there is a greater likelihood they would be.

“We live in a very safe neighborhood where kids can ride their bikes and not worry about anything,” Potter said. “For the first time, I was fearful that there was someone living in our neighborhood who was capable of incredibly irrational behavior.

“If you see something that makes you say ‘Huh,’ just call police. They can tell you if it’s appropriate.”

Potter said she first became aware of the swastika around Oct. 20 or Oct. 23, after a neighbor called her husband about it. Potter said her husband sometimes mows the community lot.

Potter’s husband, who described the mowed symbol to her and took a photo of it, said the grass in the field was a little long and the portions making up the swastika were cut close to the turf. Potter said her husband told her the swastika was roughly 40 feet across and about 40 feet tall and was unmistakably the Nazi emblem. The husband, through Potter, declined to comment or provide the photo.

A group of neighbors discussed the best way to deal with the situation, said Potter.

She said residents decided to send an emissary to the family’s home to discuss the swastika a couple of days after it was discovered. Potter said the teen’s parents admitted he had mowed the symbol into the grass. She said they were aware of his behavioral issues and were getting him treatment.

“They were going to take care of it,” Potter said. “They were aware of it.”

There was no answer at the 17-year-old’s home Tuesday, and family members previously have declined to comment.

Family and friends of the Frickers said the couple had grown so worried about their daughter’s relationship with the 17-year-old that they contacted officials at the private school the two youths attended to share their concerns about his suspected neo-Nazi views. Recently, the Frickers staged an intervention to try to convince their daughter to stay away from the boyfriend. After a difficult meeting, the girl seem to agree that would be best, said her grandmother, Janet Kuhn.

Kuhn said detectives have told the family that the fatal confrontation unfolded early Friday when her daughter and son-in-law apparently heard a noise in the home. The couple went to check on their daughter and found the boyfriend in her room, she said.

When Scott Fricker confronted him, the youth pulled out a gun and fired, Kuhn said police told the family.

Fairfax County police have declined to comment on the family’s account. On Tuesday, they said they also would not discuss how the alleged shooter may have gotten the gun.

“We aren’t releasing anything further at this point as he is a minor,” said Julie Parker, a police spokeswoman.

The police said they did not receive any reports of a swastika being mowed into grass in the Gunston Manor neighborhood in late October.

Ed Munz, president of the Gunston Manor Property Owners Association, wrote in an email that he learned of the swastika only after other neighbors had spoken to the teen’s family. He said he was not involved in the discussion about what to do about it.

Munz said neighbors were “disgusted and embarrassed” by the swastika, so they mowed the field in such a way that the swastika was no longer visible.

On Christmas Eve, Munz sent an email message to members of the community association about the swastika incident. He wrote that he hoped the swastika was not tied to the shooting in any way, but he urged people to speak up if it was.

“People who know anything of the event should step forward and speak with the police,” Munz wrote in the message.

“My hope in this is that neighbors will understand that coming forward can save people’s lives by reporting such behavior,” he wrote in an email to The Washington Post.

Peter Hermann and Ellie Silverman contributed to this report.