An elderly man killed his ailing sister and then turned the gun on himself outside their Grayson church Sunday morning, Gwinnett police said.

A third sibling discovered the bodies of Avis M. Whitley, 85, and Clarence Porter, 76, in a white 1996 Mercury Villager van in the parking lot outside First Baptist Church of Grayson in downtown Grayson.

Whitley and Clarence Porter lived at 946 Village View Circle in Loganville. Police determined that Clarence Porter had shot his sister in the head and then killed himself inside the van. Investigators said that Whitley had suffered a severe stroke several weeks ago and was in poor health.  They have not determined a motive yet for the murder-suicide, investigators said.

A third sibling, Raleigh Porter, who attends the same church, went outside looking for his sister and brother shortly before Bible study Sunday and discovered their bodies in the van, according to the Associated Press.

"I just went all to pieces," said Porter, who lived next door to his siblings. "It's heartbreaking."

Whitley's health had declined after she recently had several strokes, Raleigh Porter, 83, confirmed to the Associated Press.

"He loved her very much," Raleigh Porter said. "I think he just reached a breaking point."

Clarence Porter never married and Whitley's husband died several years ago, Raleigh Porter told the Associated Press.

"They had come in this morning just before Sunday school,” said the pastor, the Rev. Tim Brogan. “I’m still kind of processing everything.”

Brogan said the siblings had attended the 140-member church “a long time,” long preceding his four-year tenure as pastor.

He noted that the two had left behind brother Raleigh and his wife.

“We tried to find a way to comfort them,” Brogan said after learning the news.

The pastor preached a sermon about hope, but said it was difficult for church members to get through the day.

“Obviously, the mood was kind of down,” Brogan said. "We talk about this church being like a family."

Reporter Marcus Garner contributed to this report.