Just weeks out of jail, John Francis Douglas had already lost his job when his girlfriend tried to leave him for another man. The 37-year-old Prince George's County man responded Monday night by pulling out his shotgun and fatally shooting his rival, his former lover and then himself, neighbors and police said yesterday.

The double murder and suicide rattled the hamlet of Aquasco, a rural community in the southeastern corner of Prince George's County, a place where people slow down to wave when they pass on the road and violent crime is rare.

At Aquasco Supply, a general store that serves as the main gathering place in the area, people dropped by yesterday afternoon to try to find out what had ignited the events of the night before.

"I don't know that any of us will know for sure," said a man who identified himself as the owner of the store but declined to give his name. "It's just like three elements of an explosion came together at the same time. It's a real shame."

According to friends and Prince George's County police, Douglas and his girlfriend, Melvina Henderson, 47, were in the process of breaking up when she returned to the mobile home they shared in the 20200 block of Aquasco Road about 6 p.m. Monday to pick up some clothes.

Police said Henderson was accompanied by Earl Windsor, 52, of the 15600 block of Letcher Road in Brandywine, a man whom neighbors described as her new boyfriend. With them was another person, an unidentified female friend who came along to provide support, police said.

As soon as Henderson and Windsor entered the trailer, however, Douglas brandished a shotgun and fired several rounds, police said. The friend, who had remained outside, fled when she heard the shots and called 911. An ambulance crew from the nearby Baden Volunteer Fire Department arrived about 6:20 p.m. and found Windsor lying in the grass outside the trailer, with gunshot wounds to his upper body, police and fire officials said.

The paramedics spent less than two minutes treating the wounded man before they heard more shots coming from the trailer, police said. In response, the paramedics ran for cover and left Windsor behind, police said. Police arrived a few minutes later and heard still more shots coming from the residence.

And although police said they couldn't provide an exact time line of the sequence of events--including information such as how many shots were fired and when--they said the police department's Emergency Services Team stormed the trailer between 10:30 and 11 p.m. Inside, police said, they found Douglas and Henderson dead, both shot in the upper body. They said they also recovered a shotgun by Douglas's side.

Police said they were prevented from reaching Windsor, who lay bleeding in the grass, for hours because of the threat of gunfire from inside the trailer. But there were conflicting reports on how long Windsor remained in harm's way.

Police spokesman Royce D. Holloway said the Emergency Services Team rolled out an armored vehicle and pulled Windsor to safety 90 minutes to two hours after the shooting began. Windsor was taken to Southern Maryland Hospital Center in Clinton, where he was pronounced dead, police said.

But fire department spokesman Mark Brady said the ambulance did not take Windsor to the hospital until about 11:10 p.m., about five hours after the first shots were fired. Neither Brady nor Holloway could say whether Windsor was still alive when he was rescued. Both spokesmen said he was pronounced dead on arrival at the hospital.

Residents said that Henderson was a clerk at Aquasco Supply and that she had lived in the trailer directly behind the store with Douglas for at least three years. Douglas, they said, used to work at a Potomac Electric Power Co. plant in nearby Eagle Harbor, but he recently lost his job.

Friends said the relationship started to sour in the summer, when Douglas was found guilty of driving while intoxicated in Charles County and was sentenced to three months in jail. Court records show that he was released Sept. 11.

Staff researcher Bobbye Pratt contributed to this report.