MADISON, Wis. -- The grandmother of slaying victim Joel Marino told WISC-TV on Thursday that she believes a serial killer is on the loose and that the Madison police haven't done enough to find him.

Betty Parman, of East Troy, said she was on the phone with Marino the day he was killed and that he interrupted her, saying he had to go and would call her back. She said when she was on the phone she is "sure I heard the killer. I'm sure I did."

Parman said her grandson was calling to wish her a happy 75th birthday when she heard what sounded like a Halloween prank.

"Like someone came in and there was a scary 'Wooo,' and it was a man in a deep voice. And I heard it two or three times and I was just going to say, 'What is that, Joel? Is that a friend playing a trick on you?' and he said, 'I got to go.'"

Parman told WISC-TV it is was "very brief" -- maybe 10 seconds long.

She said her grandson was home doing "book work" for his job and that he had just walked his girlfriend out to her car as she went to work, picked up his mail and came inside before calling her. She said his girlfriend left at around 11:30 a.m.

Parman said that she believes Marino was working in his back office around that time, trying to catch up on work for his job.

"I don't think they came in to steal anything, unless they were surprised" by Marino, Parman said.

Parman said she's talked several times with the lead detective but is frustrated by the work being done and believes they should bring in other help, including the FBI.

"I'm very frustrated by people who are coming forward with clues and others who might be involved, and yet the police don't seem to be interested," Parman said.

She said she doesn't know how investigations go but "all I know is that I don't think this is being handled properly."

She added that even her church is "praying for the Madison Police Department."

Parman told WISC-TV that other law enforcement officials from other counties have offered help but they have been turned down by Madison police.

"Why don't they get some help?" she said. "He was such a good boy, a nice boy. It's so frustrating."