On questioning by defense attorney Susan Puhala, Monger said he had a sexual relationship with his longtime friend, Cathy Jo Newline, off and on from 1986 to 1994.
Puhala said Newline had spoken to police following the murders and said Monger had talked about the murders.
Puhala asked Monger whether he told Newline he had an alibi for the murders and that Wagner would be the "fall guy."
"I told her police couldn't get anything on me because I didn't do anything," he said.
Monger said he told Newline that "it looks like they are trying to make him (Wagner) the fall guy."
Monger said he didn't devise a scheme to kill the Davises and didn't benefit from the $50,000 insurance money each of the Davises' children received.
"She (Vivian Davis Monger) spent it while I was in prison," he said.
On cross examination by Washington County State's Attorney Ken Long, Monger said his wife received the money in 1997 while he was serving time for firearms possession. Monger said he also had felony theft and breaking-and-entering convictions.
He never confided in Newline and statements she made implicating him in the crime are false, Monger said.
"She'd rather climb a tree backwards than tell the truth," Monger said.
"How did you feel when they died?" Long asked.
"Devastated," said Monger, who grew impatient several times and snapped at Long.
Monger began to weep again in explaining that he was hurt and angry about being considered a suspect in the murders.
Daniel, 84 and Wilda Davis, 80, died Feb. 14, 1994, after being stabbed multiple times in the back and chest areas. Their bodies were found the next day in the kitchen of their 109 W. Wilson Blvd. home by a relative.
Wagner in 1996 was tried on two counts of first-degree murder in connection with the deaths of the Davises. The jury in Garrett County, Md., where the trial was moved because of pretrial publicity, failed to reach a verdict.
Wagner was re-indicted on the same charges in 2001. Prosecutors said the charges were refiled because of new applications of DNA.
Monger said he had known Wagner since 1991 and he sometimes worked with him.
Monger stopped at the Davises' home in the past to do repair work, and at times Wagner waited in his car while he went inside, Monger testified during direct examination.
In 1994, Monger owned a Chestnut Street apartment building where Wagner lived. Wagner paid about $50 a week and was sometimes late with his rent, Monger testified.
Monger also rented rooms to William Hasenbuhler, who he evicted in the weeks prior to the murders because he didn't like the company Hasenbuhler was keeping, he said.
When Hasenbuhler left, "he threatened to come back and get even with us," Monger said.
Monger testified that he had seen a knife like the murder weapon in Hasenbuhler's possession prior to the murders.
The day of the murders, Monger said he was out running errands and arrived home between 7:05 and 7:10 p.m. and had forgotten to pick up potato salad at the Davises as was prearranged.
When talking about the Davises' deaths, Monger's face began to turn red and he burst into tears. He took his glasses off and sobbed for a few minutes before composing himself and answering more questions from Puhala.
After finding he arrived home without the potato salad, Vivian Monger called her mother to see if Ted Monger should return for it but there was no answer, Monger testified.
The next day, Monger said he drove to the Davises' home in the early morning to drop off some dishes and pick up the potato salad but no one answered the door.
Testimony is expected to continue Monday.