(CNN) -- A Pennsylvania district attorney says there may never be closure in the case of a man suspected of killing his ex-wife and five former in-laws.

"There's no excuse; there's no valid explanation. There's no justification for snuffing out these six innocent lives and then injuring another child. This is just a horrific tragedy," Montgomery County District Attorney Risa Vetri Ferman told reporters Tuesday.

The body of the suspect, Bradley William Stone, was found with what looked to be self-inflicted wounds.

The former Marine reservist had been on the run since Monday's slayings shook small communities north of Philadelphia.

Although a final report from the coroner is pending, Stone appears to have died from self-inflicted cutting wounds, in the center of his body, according to Ferman.

His body was found in a wooded area about 1/2 mile from his home in Pennsburg. It was not immediately clear how long the remains had been there.

"When you look at the three different locations, the number of people killed, clearly we are looking at a premeditated killing -- a planned killing, an intentional, deliberate killing," said Ferman.

The slayings

The killings broke the calm in several small towns in Montgomery County, the second wealthiest county in Pennsylvania and the 51st wealthiest in the United States, according to the county government web page.

Early Monday morning, a hangup call to 911 first tipped off police to the bloodshed, directing them to Lansdale, 28 miles northwest of Philadelphia.

When police arrived, they found two slain women: Stone's former mother-in-law and former grandmother-in-law, Ferman said.

A short time later, a neighbor of Stone's ex-wife called 911, the prosecutor explained. Police went to an apartment in Lower Salford and found 33-year-old Nicole Stone dead.

"I heard three or four gunshots and I heard the kids yelling, saying, 'Mommy, no. No, mommy, no.' And he just said, 'Let's go. We gotta go,'" a neighbor who did not want to be identified told CNN affiliate WFMZ. "I heard him say, 'Let's go. We gotta get in the car.'"

"They didn't have any coats on or anything," the neighbor said. "They just had their pajamas on, and he just said, 'We gotta go.' He was like, 'She's hurt. She's hurt pretty bad. We have to leave.' And just got in the car and sped off."

In addition to Nicole Stone, her mother, grandmother and sister were found dead, as well as the sister's husband and 14-year-old daughter, Ferman said.

The sister's 17-year-old son was being treated at a Philadelphia hospital. Ferman said that the teen, who sustained cutting injuries to his hands and head, was in serious condition.

But Stone didn't harm his two daughters, who were living with his former wife. At about 5:30 a.m., he brought them to a neighbor's residence in Pennsburg, according to Ferman.

"That was the last time he was seen by anyone," the attorney said. "I think it's of great significance the children are safe right now."

Ferman said Stone and his ex-wife had been involved with ongoing and contentious custody disputes.

"We learned that just last week he had made an effort in court to try to secure custody -- emergency custody of the children -- and that was denied," she said.

Who is Stone?

According to Montgomery County court documents found online, the Stones divorced in 2009.

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Stone served as a reservist in the U.S. Marines until 2011, mainly as a meteorologist, according to the Marines. He spent a few months in Iraq in 2008.

William Schafte of Harleysville, who described himself as a friend, called Stone a "caring guy" who loved his country.

"I was totally shocked. I didn't really think that he was capable of doing such a horrific thing like this," he told CNN's "The Lead with Jake Tapper."

"He would ... go the extra mile to help anybody out. This is just, it's a total shock to me and to his other friends."

Stone served as president of the American Legion William E. Hare Post 206 in Lansdale about a decade ago, said current post commander John Gillmer, the Morning Call newspaper of Allentown reported.

"He was always on the honor guard and stuff like that for parades," Gillmer told the Morning Call. "I couldn't believe it. ... I never would have thought it was one of our guys."

The Upper Perkiomen School District called off classes Tuesday. Following the announcement of Stone's death, it said schools would reopen at regular times Wednesday.

CNN's Shimon Prokupecz, Susan Candiotti, Ed Payne, Ralph Ellis, Kristina Sgueglia and Lawrence Crook contributed to this report.