HENNEPIN — A carpet cleaner that had been characterized as a key piece of evidence against accused murderer Clifford Andersen Jr. turned into a possible defense asset Tuesday during his continuing trial in Putnam County.

An eyewitness had seen the Standard man carry the Bissell cleaner into the vacant home where he allegedly killed sister-in-law Deborah Dewey, and a police forensic scientist testified Tuesday that blood traces were found on some parts that were not clearly visible without taking the unit apart.

But the significance of the machine appeared to be undercut by a crime scene investigator’s acknowledgment that the Standard home’s carpet did not appear to have been cleaned, even in areas where there were apparent blood stains.

Andersen, 68, is standing trial on charges of first-degree murder and concealment of a homicidal death. He allegedly beat the 62-year-old Ladd woman to death and then buried her in a shallow grave outside the vacant house, to which he had access as longtime caretaker.

Kevin Zeeb, a recently retired Illinois State Police forensic scientist who had been working in the agency’s Morton crime lab at that time, observed that the cleaner as a whole was exceptionally clean when examined. But blood was detected on the inside of the wheels after he removed them and also in a slot that held a post attached to the base of the machine, he said.

In separate testimony, ISP crime scene investigator Darrell Stafford cited a large apparent bloodstain in the living room carpet as one of many types of possible evidence found after Andersen was arrested. Others included signs of blood on the carpet in a storage room and about 50 apparent spatter spots on a wall and an old door leaning against it, he said.

But on cross-examination, co-defense attorney Drew Parker zeroed in on Stafford’s testimony that the carpet was matted in the area of the stain and items like a screw, hairs, maggots and general debris were found on or near it. He asked if there was any evidence of attempts to clean the stain with a cleaner.

“Not to my knowledge,” Stafford said.

Nor did chemical tests reveal any attempts to clean the spatter marks, Stafford acknowledged. But that did not necessarily mean that there had been no efforts to clean up the scene, he insisted.

“You could clean some and leave some evidence,” he said.

In other testimony, a forensic entomologist narrowed Dewey’s time of death to a period including the Aug. 22 date when she was last seen alive and prosecutors allege Andersen killed her. But she did not pinpoint that date.

Relying on the stages of development of insect larvae when Dewey’s remains were unearthed on Sept. 12, Amanda Roe concluded that insects had access to the body by no later than Aug. 30 or 31. But because that access would have been delayed by the body being tightly wrapped in a tarp secured with ropes and duct tape, the time of death could have been up to 10 days earlier, she indicated.

Asked specifically about Aug. 22, she replied, “There’s nothing in the evidence to exclude that date.”

Jurors also saw numerous photographs of the grave where Dewey’s body was found buried in manure, with the surface newly seeded to grass and covered with straw and freshly cut branches. It was as shallow as five inches in some parts, Stafford testified.

“The deepest point in the burial site was 13 inches,” he said.

In earlier follow-up testimony on a different topic, a state police criminal analyst tried to clarify confusion arising from her testimony Monday about calls between Andersen and Dewey on Aug. 22.

Lynn McCloskey said one of two printed reports cited Monday had the times from cellphone company records standardized to central time while the other did not. But she had also said Monday that there were 10 calls, whereas prosecutors have said there were only five.

She said initially on Tuesday that two of the calls were actually one that involved two towers operated by different carriers, so there were nine calls but 10 records of connection. But on further cross-examination, she appeared to back away from the word “calls” altogether while repeatedly emphasizing that her reports were based entirely on phone company data.

“I have not drawn any conclusions,” she said. “These are the records of the phone companies.”

The trial will continue Wednesday with witnesses expected to include a state DNA expert.

Gary L. Smith can be reached at (800) 516-0389 or glsmith@mtco.com. Follow him on Twitter @Glsmithx.