A retired St. Paul police sergeant who interviewed Jeffery Trevino in connection with his wife’s disappearance and death is expected to take the witness stand Friday afternoon, capping prosecutors’ witness list for the trial.

Jurors could begin deliberating the case on Tuesday, Ramsey County District Judge Leonardo Castro said. Retired Sgt. John Wright will be the prosecution’s 42nd witness; it’s unclear how many witnesses, if any, the defense will call.

Also unclear is whether Trevino will testify, but he must decide by Monday whether he’ll take the stand. Trevino, 39, faces two counts of second-degree murder for allegedly killing his wife, Kira Steger, 30. She was last seen alive Feb. 21, and her body was recovered May 8 from the Mississippi River.

Prosecutors believe Trevino killed Steger in a jealous rage because she was having an affair with a co-worker and wanted a divorce.

The sixth day of testimony in Trevino’s murder trial resumed Thursday afternoon with defense attorney John Conard’s cross-examination of a DNA scientist who tested several spots of suspected blood from the alleged crime scene and two cars.

McKenzie Anderson, a DNA scientist with the Minnesota Bureau of Criminal Apprehension (BCA), testified Wednesday that several spots of suspected blood from the couple’s master bedroom, other areas of the home and Steger’s car trunk matched Steger’s DNA.

The interpretation of forensic evidence is Conard’s key strategy, and he’s aggressively questioned other scientists who have testified. He questioned the BCA’s decision to test only some of the suspected blood evidence collected from the couple’s house in the 500 block of Iowa Avenue E.

Conard cross-examined Anderson on Thursday, addressing complications presented by diluted samples and mixed DNA results. He asked Anderson if DNA can remain on surfaces for a long period of time, not just around the time evidence was collected.

Anderson said yes.

He asked whether in some mixed samples, a small percentage of people from the general population could be contributors.

Anderson said yes.

Conard noted that professional standards recommend that scientists compare test results to DNA profiles they haven’t seen before. He then asked Anderson when she first came to know Steger’s DNA profile.

“It was early on,” Anderson said.

Conard asked whether she knew Steger’s DNA profile before she tested the suspected blood evidence collected from Steger’s home and car.

Yes, Anderson said.

Anderson testified that no blood was found on a sweatshirt and sweatpants belonging to Trevino that he was allegedly wearing when he fueled Steger’s car around 2 a.m. on Feb. 22, the day she went missing. Video surveillance shows a car matching Steger’s turning left from the station toward Interstate 35E instead of right, the quickest route to the couple’s home.

Prosecutors have implied that Steger’s body could have been in the trunk that morning, and was on its way to being dumped.

Anderson also testified under cross-examination that there’s no way of knowing whether DNA came from blood or other sources, like skin cells. Another BCA scientist previously testified that preliminary tests showed the presence of blood on several locations throughout the home and cars.

When testimony ended Thursday, Castro told Conard that he if he was going to present an alternate perpetrator theory for Steger’s death, he needed to establish some foundation.

Conard didn’t divulge his strategy, but said, “I don’t think you have to worry about me messing up the trial.”

Testimony resumes at 1:30 p.m. Friday.