A Bridgeport woman found her sister and brother-in-law dead Wednesday night in what police are describing as a murder-suicide.

They say Keith Knox, 32, killed himself after gunning down his wife Jennifer, also 32, in an apartment building on the 400 block of Trumbull Avenue.

"On something like this, there's absolutely nothing that you can do," says Bridgeport's police chief, AJ Perez. "The only thing you can do is pray for them, and you pray for their families."

Police say Keith Knox worked as a security guard and firearms instructor and had a permit for the gun he used.

Friends, relatives and other mourners set up a growing memorial outside the couple's apartment.

"My daughter was so sweet," says Madeline Gonzalez, Jennifer Knox's mother. "She helped anyone. She was always smiling."

Mohammed Hamid, a neighbor, says the last time he saw the couple was on Tuesday -- and it was the only time he says he had ever seen evidence of discord between them.

"They came, slammed the car doors, and went inside," Hamid says. "And they seemed like they were arguing."