Investigators nearly from the start considered Derrick James Jackson the main suspect in the October 2022 murders of his 62-year-old mother and her 65-year-old partner, a detective who worked the case testified Thursday.  

The circumstances of Jackson’s arrest, which came several hours before the discovery of the bodies of Tricia DeMotts and Stanley Grotberg, prompted investigators’ interest in him, said Luke Foster, then a detective sergeant with the Flathead County Sheriff’s Office. 

“The ... fact that he was located with what we believed to be most likely the murder weapon, the fact that he was wearing Stanley's clothing directly after we believe this [double homicide] occurred,” Foster told jurors in Flathead County District Court. “All of this together led me to believe he likely committed the act.” 

Prosecutors have charged Jackson, 39, with two counts of deliberate homicide and one count each of tampering with evidence and criminal possession of dangerous drugs in connection with the deaths of DeMotts and Grotberg. The couple was found shot to death in their Esteban Lane home in Bigfork during an Oct. 28, 2022 welfare check. 

Jackson pleaded not guilty before Judge Amy Eddy in February 2023. Deputy county attorneys Amy Kenison and Katie Handley are prosecuting the case. 

Living with DeMotts and Grotberg at the time, Jackson was arrested after he allegedly attempted to break into neighboring homes on Esteban Lane. While taking him into custody, deputies found a bottle of prescription medication made out to Grotberg in his possession. They also found a magazine clip on him, leading to a search of a nearby grassy area. 

That turned up the .40-caliber Smith and Wesson pistol that investigators believe was used to kill DeMotts and Grotberg.  

Much of Thursday’s testimony came from experts with the Montana State Crime Lab, who reviewed evidence submitted by investigators. Jurors learned that the gun and two magazines associated with it were unsuccessfully checked for Jackson’s fingerprints.  

But a Smith and Wesson gun case found in Grotberg’s Nissan Pathfinder, which was parked outside the couple’s home, did feature a match for Jackson’s hand, testified Stephanie Shappee, a forensic scientist with the crime lab.  

A second forensic scientist, Doug Lacon, testified that he compared casings recovered at the murder scene with those he retrieved while test firing the Smith and Wesson. Markings left on the base of the cartridges indicated that they were fired from the same gun, he said. 

Travis Doria, an expert on primer gunshot residue, testified that residue was found on the hooded sweatshirt and blue jeans Jackson was wearing when he was arrested. And Joe Pasternak, a DNA analyst for the state in 2022, said he found likely matches for Grotberg’s DNA on Jackson’s clothing and the Smith and Wesson as well as on samples of blood taken from the couple’s Esteban Lane home.  

DEFENSE ATTORNEYS Thomas Schoenleben and Levi Roadman continued their efforts Thursday to paint the investigation into the double homicide as myopic, focused on proving Jackson the killer from the get-go.  

While cross-examining forensic experts from the state crime lab, they noted that investigators only asked the lab to look for Jackson’s fingerprints on evidence collected in the case, and that they failed to submit the victims’ clothes for analysis — for gunshot residue in particular.  

They also sought to demonstrate that the forensic analysis stopped short of showing that Jackson fired the bullets that killed DeMotts and Grotberg.  

Over the course of the trial, which began March 31, Jackson’s defense attorneys have raised the possibility that Grotberg was a source of abuse in the home and suggested that Jackson may have acted in self-defense.  

In a recording of a conversation Jackson had with his father in the county jail following his arrest, Jackson allegedly made mention of trying to avoid being killed and saying he had defended himself. 

While cross-examining Foster, Roadman noted that detectives investigating the case in October 2022 were working without the analysis later provided by the crime lab.  

“There was never any other suspect in this matter?” Roadman asked.  

“No,” Foster said.  

“That's how the investigation was conducted, with one suspect?”  

“Correct,” Foster replied. 

Investigators, Roadman posited, determined Jackson was their suspect within hours of his arrest.  

Under redirect from Kenison, Foster said that was a common occurrence.  

“Oftentimes when we’re investigating crimes, there’s one suspect,” he told jurors.   

News Editor Derrick Perkins can be reached at 758-4430 or [email protected].