Eagleville, Pennsylvania: The body of an Iraq War veteran suspected of fatally shooting and stabbing six family members in Pennsylvania was discovered on Tuesday following a two-day manhunt, a district attorney said.

Suspect Bradley William Stone, 35, of Pennsburg was being sought in the deaths on Monday of his ex-wife, her mother, grandmother, sister and two other family members, including his 14-year-old niece.

'He went away to Iraq and came back and was a completely different man,' said a neighbour who knew the shooter. 

Montgomery County District Attorney Risa Vetri Ferman said she and other law enforcement officials would hold a briefing regarding the discovery of Stone's body.

Police during the manhunt for Bradley William Stone. Photo: AP

The manhunt prompted lockdowns and cancellations of schools around Pennsburg, about 80 kilometres north-west of Philadelphia, and residents had been advised to stay inside with their doors locked.

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The killings began hours before daybreak, and sent SWAT teams scrambling from town to town and put schools into secure mode. Officers discovered bodies in homes in Souderton, Lansdale, and Harleysville, in Lower Salford.

Besides Nicole Stone and her mother, JoAnne Hill, the victims were Nicole's grandmother, Patricia Hill, 75, her sister, Patricia Flick; her brother-in-law Aaron J. Flick, and her 14-year-old niece Nina Flick. Anthony Flick, 17, Nina Flick's brother, was airlifted to Jefferson Hospital, where Ms Ferman said he is in very serious but stable condition with family at his side.

Police search for Bradley William Stone in Pennsburg, Pennsylvania. Photo: AP

Stone's daughters, ages 8 and 5, were not harmed. He had taken them from his ex-wife's house and left them with a neighbour on Monday, Ms Ferman said. His current wife and infant child also were safe.

The killings set off Pennsylvania's second recent high-profile manhunt after a seven-week chase to capture survivalist Eric Frein, 31, who accused of killing a state trooper in September.

Schools in the Pennsburg area were closed on Tuesday, the district said.

Bradley William Stone, the former US Marine and Iraq war veteran accused of murdering his ex-wife and five members of her family was found dead in the bush near his home on Tuesday. Photo: AFP

Stone suffered from post-traumatic stress disorder, the Bucks County Courier Times reported. He enlisted with the US Marine Corps Reserves in 2002, was deployed to Iraq and was honourably discharged at the rank of sergeant in 2011, according to a military spokesman.

Autopsies were under way on Tuesday. A law enforcement source said some of the bodies had stab wounds, some gunshot wounds and some may have had both.

Stone and his ex-wife, Nicole, 33, filed for divorce in 2009 and continued to have a custody battle. Stone asked a court on December 5 to grant him custody on an emergency basis, according to court records.

Lisa Andrey, a longtime neighbour of Nicole Stone's mother, said the couple had "a very volatile relationship" that deteriorated after the Marine returned from Iraq.

When the pair first got together "he was a great guy and an excellent father," Ms Andrey said. "And then he went away to Iraq and came back and was a completely different man."

In a statement, the Marine Corps confirmed Stone served between 2002 and 2008. His four service medals included the Global War on Terrorism Service Medal and the Iraq Campaign Medal.

Among the Facebook groups that he appeared to list among his favourites were pages for local and national veterans groups and the National Centre for Post Traumatic Stress Disorder. Court records also show Stone had three  drink-drive arrests, and was on probation for one conviction.

On Tuesday morning (local time), Stone's house in Pennsburg remained open, the doors off the hinges.

Inside there was a half decorated Christmas tree and a bookshelf with photos of children and a collection of mystery novels.

Reuters, TNS