Mass Murderer
Bradley William Stone, a 35-yr-old Pennsburg, Pennsylvania resident is pictured in this undated handout provided by the Montgomery County District Attorney's Office. Stone is suspected in the deaths of six people and the serious wounding of another at three locations in Montgomery CountyReuters

Police officials in Pennsylvania's Montgomery County have been on a manhunt since Monday for a suspect believed to have shot dead six people earlier in the day outside Philadelphia.

The suspect, identified as Bradley Stone, a 35-year-old Marine who had served in Iraq, reportedly killed his former wife and some of her relatives, including her 14-year-old niece, and is said to be still armed, according to police officials.

Residents have been asked to remain indoors and lock doors and windows, as the manhunt stretched into the second day. Schools on Upper Perkiomen School District have been closed for the day as the suspect remains at large. 

SWAT teams moved the search for Bradley to Bucks County, after reports of a man carjacking at knife point emerged, according to the Lehigh Velley Express Times.

Among the dead who were found in their homes outside Philadelphia were Bradley's former wife Nicole Stone, her mother and grandmother and her sister Patricia Flick and her family. Flick's 17-year-old son was wounded. 

Nicole was found dead in her apartment in the Harleysville section of Lower Salford Township. Neighbours said they heard gunshots from the apartment and then saw Bradley running away with his two children. 

He reportedly dropped off his daughters at a neighbour's home before disappearing. 

The murders are believed to be linked with domestic issues between the couple who had filed for divorce in 2009 and had been engaged in a fight over the custody of the two children.