(CNN) -- A forensic consultant for the defense of a former Kansas police officer accused of killing his wife testified on Thursday that evidence showing the man had gasoline on his pants could have been contaminated.
Brett Seacat is on trial for the first-degree murder in the death of his wife, Vashti. Prosecutors say he shot his wife in April 2011 and set their home on fire, but the defense says Vashti was depressed and committed suicide after torching the house.
Pants collected from Brett Seacat the morning of the incident weren't placed in the appropriate bag, according to Gene Gietzen, the forensic consultant.
Investigators on the scene placed the pants in a paper bag and transferred them to a plastic bag about an hour later. Gietzen says an unlined paint can or a nylon bag is the appropriate transport method for any evidence that may contain an accelerant -- in this case, gasoline. Paper and plastic bags allow the accelerant to escape and can even let accelerant present in the air cross-contaminate evidence, according to Gietzen.
Gietzen showed the court notes written by Chris Riddle, the forensic scientist from the Kansas Bureau of Investigations who worked on the case. Riddle appeared to have concerns about the packaging of the pants, writing, "Not sealed properly for fire debris analysis!"
Monte Weldon, a neighbor of the Seacats, also testified on Thursday that he was shocked to learn the couple was splitting up. He approached them in their driveway the day before the incident, wanting to know what he could bring to a barbecue that was originally scheduled for the day Vashti died.
Before Weldon could even ask the question, he said, Brett Seacat told him the party was off because the couple was divorcing. Weldon said that Seacat didn't seem to be angry or enraged and that he wasn't making any secret of the couple's separation.
Weldon also testified that Brett Seacat had plans to fix up the home, so he was surprised to hear that Seacat was being accused of burning it down.
Weldon said he sold sand and dirt to Seacat to build a sandbox and to fill in a hole in his yard. Seacat was also planning to change out all of the light switches in the home, Weldon said.
"It was such a beautiful house, you couldn't help but talk to him about it," said Weldon. "He loved the house."
Seacat has said he was sleeping downstairs on the night of the fire, HLN affiliate KWCH reported. He heard a noise, and moments later, his wife called him on his cell phone, saying he should get their two boys out of the house before they got hurt.
He then purportedly heard two pops. Brett Seacat went upstairs and saw flames.
He reportedly said he found his wife in their bedroom and tried to save her.
Prosecutors say Brett Seacat's story doesn't make sense.
For one, he had no soot or blood on him, they say, according to KWCH, and only a small burn on his foot.
He and the couple's sons escaped from the blaze unharmed.
The Seacats' home in Kingman, Kansas, sits not far from the courthouse where Brett Seacat is standing trial.
Despite extensive fire damage, the house still stands; a brick chimney pokes out of the charred remains.
"I'm smart enough that if I wanted to kill my wife ... I could've come up with something better than this," Seacat told investigators about the shooting and the fire.
"This is what a crazy person does."