"My heart is just breaking for their family and their friends," Patricia Dudas said.
She added later about her son, "I will never, ever stop loving him."
"It's hard," said Dudas' father, Michael.
Dudas' parents, younger brother, and two younger sisters live next door to where Ferguson lived. Ferguson's mother, Marjorie, answered the door at her home in Coatesville but declined to comment Thursday.
Merritt Dudas is being held at the Chester County Prison on first-degree murder, robbery, and other charges. Patricia Dudas said her son had called his family Wednesday from prison. They spoke briefly, and the parents said they were relieved to hear their son's voice.
"He's very despondent," Dudas said of her son. "He feels like he doesn't deserve anybody's love and support, and I basically said, 'Well, you're getting it anyway.' "
Dudas said she was grateful that neighbors and friends have stopped by the house to offer support.
She said her son has struggled with drugs for the last 10 years and has been in and out of rehab. He was diagnosed with depression after his uncle committed suicide in 2005, and it was then, the parents said, they saw a change in him. They said he was recently trying to get his life back on track.
"He was always such a loving, caring, thoughtful child," Dudas, 47, said. "It's a shame this is what happens with drugs."
The parents talked about their son in their one-story home, where pictures of their four children hung on the walls. They brought out a graduation photo of a smiling Merritt in a suit and tie. That's the son they know, they said, not the grim one in the mug shot.
They remember their son as a funny and artistic kid who loved to cook and surprise his family with dinner. They know him as remembering every wedding anniversary and adopting their pet Chihuahua Rat Terrier mix, Nacho, as a Christmas present.
Dudas said she had not seen her son since late August or early September. She said she did not know that her son and Ferguson, both of whom attended Great Valley High School, still talked and does not know what had happened between them.
Police said they found Ferguson's body Monday afternoon inside a sleeping bag in his home's detached garage, after his mother reported him missing.
Merritt Dudas hid the body there after shooting him and drove away in Ferguson's car with his wallet and phone, police said. They said they found the stolen items and the .380-caliber Ruger handgun used in the slaying at the Montgomery County home where Dudas was living with his girlfriend.
Dudas was convicted of burglary, trespassing, and marijuana possession in 2008 and was not permitted to carry a gun.
His preliminary hearing will be within the next week, police said.
The killing is the first reported in Malvern since a domestic dispute in 1996.