An attorney for Ates claims that in 2006, the 62-year-old who stood 5 feet 8 and tipped the scales at 285 pounds was in such bad physical shape that couldn't have pulled off the shooting or the fast getaway the killer made.
Ates' attorney Walter Lesnevich said his client's weight has caused Ates' asthma, sleep apnea and other obesity-related ailments.
"You look at Ed and you don't need to hear it from a doctor," Lesnevich said.
Houston defense attorney David Berg, author of "The Trial Lawyer: What It Takes To Win," an analysis of trial tactics and strategies, said that he had never heard of such a defense but that it could work.
"It's an unusual defense, but it would be a credible defense if the facts really fit in," Berg said.
"When the battered-wife defense was first used, it was considered abhorrent and bizarre," Berg said. "Jurors may be open to this in a society that talks about the infirmities that that obesity causes."
At the time of the killing, Duncsak and Ates' daughter, Stacey, were involved in a bitter custody dispute after their 2005 divorce.
Prosecutors claim Ates drove from Fort Pierce, Fla., to Duncsak's $1.1 million home in Ramsey, about 25 miles northwest of Manhattan, in August 2006 and shot him as he came home from work.
Duncsak was talking to his girlfriend on his cell phone when he entered the house and was shot. After hearing a scream from him, followed by a thud, the woman called 911. Police arrived minutes later, but the killer was gone.
Police quickly suspected Ates and found him 24 hours later at his mother's home in Sibley, La.
According to Lesnevich, the trajectory of the bullets shows that Ates wasn't physically capable of the shooting.
Duncsak was shot six times as he walked down a hallway. Lesnevich said the shooter first fired from a staircase leading to the basement. That was followed by several shots fired head-on. In order to do that, Lesnevich said, Ates would have had to run up the stairs.
Lesnevich also says it would have been impossible for Ates to clean up all the shell casings and flee the house before police arrived minutes later, let alone to have driven alone 21 hours straight to his mother's house in Louisiana.
Prosecutors have built their case around cell phone records and computer forensics and have little physical evidence. Still, they say they have a strong case.
During the trial, they have presented evidence to show Ates bought books detailing how to build a gun silencer, did Internet searches on how to pick locks and how to commit the perfect murder.
Duncsak's mother, Sophia, has said Ates became vengeful toward her son after Paul Duncsak refused to give his father-in-law $250,000 in 2003 to keep Ates' struggling golf course in Okeechobee, Fla., afloat.
And Ates' sister testified that she initially told detectives her brother arrived at their mother's house a day earlier then he did because he asked her to lie.
While obesity appears to be a rare strategy for a murder trial, the defense was used recently in Ohio by double murderer Richard Cooey, who argued that he was too fat to execute.
He argued that at 5 feet 7 and 267 pounds, his obesity made death by lethal injection inhumane because it would be difficult for prison staff to find suitable veins to deliver the deadly chemicals. There were no such difficulties when he was executed this month.
Possibly hurting Ates' argument for jurors: He lost 40 pounds while in jail awaiting trial.
"It visually impacts it," Lesnevich said. "I'm probably the only person in his life that told him not to lose weight."