The Murder

Cottonwood is known for its beautiful countryside, quaint, small-town charm, and family atmosphere. On May 4, 2012 Robinson Glen Drive appeared to be just another quiet street in this rustic town with nice homes and families. But on May 5, 2012 life on the street changed.

The road accustomed to bicycles and basketball hoops was suddenly filled with ambulances, deputy patrol cars and undercover detective units.

The blue, one-story, home at the end of the street, was now the scene of a grisly homicide. Crime scene tape was wrapped around the trees in the front yard. When daylight broke, those who hadn't already been roused in the neighborhood by all the commotion began asking questions. But so early in the investigation, law enforcement had little answers.

By the end of the day detectives told local media it was a homicide case. A woman had been killed in her home. That woman was 51-year-old Karen Duenas.

She lived in the home with her husband, Mark, and their son Casey. Mark and Karen had five sons; they had lived in Cottonwood for years and were a large presence in the community. The couple's son Jason and his family lived next door.

But Karen was more than just a wife, mother, and grandmother. She was also an instructor at Shasta College and had recently become a nursing student at the college too.

On that early May morning she was found stabbed to death in her bedroom, once in the chest and twice in the back. Detectives said when they arrived to the home Karen was propped on pillows lying in a pool of blood. A bloodied blanket at her feet, her face and hands, however, had been wiped clean from blood. Karen slept alone in her room, her husband slept down the hall in a different room. The couple had slept separately for years because of Mark's strange work schedule with UPS.

The morning of the murder Mark told investigators he awoke to what sounded like cats fighting. He got up and looked around; when he didn’t notice anything he walked to Karen's room. That's when he discovered his wife face down in blood. He said he heard a fluttering and gurgling sound coming from her chest. Mark said he immediately went to wake his son Casey and told him to go next door and get help from his firefighter in training brother, Jason. As Casey went next door, Mark called 911. He told the dispatcher he needed help and that there was blood everywhere. Shortly after the call, Shasta County Sheriff’s deputy Troy McCoy arrived on scene. Once he determined the home was safe he allowed paramedics inside who determined Karen was dead.

From that moment on the family of Karen and Mark Duenas would never be the same. They had just lost their mother and matriarch of the family. Now, more than ever, they would have to stick together to get through this difficult time.

The Investigation

The day Karen was found stabbed to death no one was arrested for the murder. Days after the incident investigators slowly began to release more information about what happened. They also asked for the public's help. They were looking for any tips, any leads to who could've killed Karen Duenas.

Divers from the Sheriff's Department searched the ACID canal which was a few blocks from the home. Members of the Search and Rescue team combed the neighborhood.

Investigators would never say what they were searching for but just days after the murder they said they hadn't found anything. People in the neighborhood, the community, even the county began talking amongst themselves, forming their own opinions into what happened.

Was there a crazed serial killer on the lose?

Should the public be worried?

According to a Sheriff’s detectives the answer was no.

“I urge the public to have trust in the Sheriff's Office. I mean I have family and friends that live in this neighborhood as well and based upon our original statement the public in general is not at risk our office still stands by that.”

Several days went by following the detective's reassurance.

11 days after she was found stabbed to death in her home, Karen's husband Mark, was named a person of interest. Then, months go by where seemingly nothing happened. Mark continued to live at his home with his son but behind the scenes there was a flurry of activity with detectives and criminalists pouring over evidence.

On July 19, 2012, three months after the murder, lead detective Logan Stonehouse provided an explanation for the lack of public information. “What you see on TV the results you get back in a day. That's just not how it is out here in the real world it takes a long time for these results to come back, for the DNA process to come back. It takes weeks, if not months, if not years.”

And then the waiting ended, exactly five months after the murder. On Oct. 5, 2012, Mark Duenas was arrested at his home in Cottonwood for Karen's murder. Shortly after the arrest the Shasta County Sheriff’s Office released details about their investigation and why they believed Mark was guilty.

Investigators said Mark told them at one point he was in a phone relationship with another woman, named Annette Green. She lived in Idaho but grew up in Shasta County. The two knew each other in high school but never dated. They reconnected through one of Mark’s coworkers on Facebook and began texting and occasionally talking on the phone.

When Karen found out about the relationship she was hurt and asked Mark to stop talking to Green. However, he bought a track phone and continued to speak to Green. Green told investigators Mark at one point had told her, “Something bad would have to happen for us to be together.”

Investigators said Mark had staged a phony break-in to the home the night of Karen’s murder. However he made mistakes in his efforts. They said there were no signs anyone else had been in the room. Dust on the window sill was untouched and there was furniture blocking the window where a person could potentially exit. They also said the plants under the window were unharmed. Nothing was missing from the room to indicate it was a robbery.

Karen suffered three stab wounds. One large gash to her chest and two to her back.

Investigators said there were no signs of a sexual assault.

Investigators said another sticking point in Mark’s guilt was the 911 call he made in the moments after discovering his wife. They claim he said, “I found my wife shit, blood everywhere.” They described Mark’s behavior as strange in the hours after her body had been discovered and when deputies began securing and searching the home. They said he lay on the couch with a blanket covering his face, seemed to be sleeping and asked the deputies if they had found anything outside.

On Feb. 19, 2013 the family spoke about the case for the first time outside the Shasta County Courthouse, saying they supported Mark.

Some 20 family members from Mark and Karen’s family came to support him at a trial readiness conference.

Her family standing behind her, Karen’s older sister Jennifer Regelin spoke to the media, “The Tenney family would like to say they continue to give love and support to Mark Duenas, his five boys and their families.”

A separate statement was also released by Mark and Karen’s son speaking out against how their father has been portrayed.

They said the belief that the couple’s marriage was crumbling because of an out-of-state phone relationship was false.

Mark’s attorney, Ron Powell, read the statement on their behalf.

“We were aware of this relationship, including our mother, while she was not thrilled about it our parents were still very much in love.”

“Our dad is a caring loving man that was deeply in love with our mother and misses her everyday just as we all do.”

A Hung Jury


Opening statements for Mark’s trial began on July 11, 2013. After two days of jury selection, a jury consisting of seven women and five men were seated. Shasta County Deputy District Attorney Eamon Fitzgerald represented the people, while Mark was represented by Ron Powell, from Rancho Cucamonga in Southern California. On the first day of trial, the other woman, Annette Green testified about her relationship with Mark, this was the first time the two had seen each other in person since the seventies.

She said they began talking in 2011. At first they caught up on life but eventually they began expressing feelings for each other. The two never saw each other or had a physical relationship. After a few months she told Mark she was beginning to feel guilty and they stopped talking.

Mark contacted her a few months before Karen’s murder to tell her happy birthday.
In a cross examination, Powell reminded the jury that the relationship had never been physical, that the two often talked about their families, that Mark had told Annette he loved Karen, at one point saying, “He would need to be a better husband.”