Bradley says it was her idea to take the test.
"I told them it's not possible," Bradley said. "It's absolutely not possible."
Former FBI Agent Jennerich explains how and why Bradley may have failed.
"A test like this is a polygraph examiners worst nightmare," Jennerich said. "It's so emotional. It's so traumatic for the parents. Even if the parents was not involved at all, they can still feel responsible because they can feel they didn't properly protect the child."
Jennerich gives polygraph tests independently now and he's seen the tests set innocent people free and cause guilty people to confess. He says this case is different.
"This is the worst type of poly you can ever be asked to administer to a person because of all the emotion involved in this case," he said.
Some people feel it's an effective tool for investigators. It's not always conclusive and that's why it's often not admissible in court.
"She failed for one of two reasons," he said. "Either because she is guilty of lying to the relevant questions or she is under such a traumatic experience that she feels guilty for not taking care of her child even if she had no direct involvement in the disappearance of the child."
Yellow ribbons surround trees in the neighborhood where Lisa Irwin disappeared. Her parents say they don't care what people think, they just want their baby back.
If you have any information on where Lisa Irwin is, please call police or the TIPS Hotline at (816) 474-TIPS.