A murder-suicide that claimed the lives of four Garfield Township family members appears to have been the result of a deliberate, “pre-meditated” act by one or both parents, according to the Michigan State Police.

At a press conference Monday, Lt. Kip Belcher shared new details on the investigation into the August 11 deaths of 54-year-old Jeffrey Allen Mendenhall, his wife, 34-year-old Tamisha Marie Mendenhall, and their two children, 6-year-old Thomas and 3-year-old Olivia. The family members were discovered inside their home on Shady Lane in the Town and Country mobile home park on August 13 after troopers conducted a welfare check at the residence. A concerned co-worker at Munson Medical Center reported that Jeffrey had missed multiple days of work.

[Warning: Some of the following details are graphic and disturbing]

The bodies of the two children were discovered inside a bedroom “peacefully posed together” holding stuffed animals and flowers, according to Belcher. Jeffrey, also holding flowers, was found lying in a hallway with his head resting on a pillow in the doorway of the bedroom where the children were discovered. Neither Jeffrey nor the children suffered any traumatic physical injuries.

Tamisha, who Belcher said was the “last person” alive in the home, was found lying a few feet from her husband in the hallway. She died of a single, self-inflicted stab wound in the groin area that pierced her femoral artery.

Belcher said a helium tank, empty prescription bottles of Benzodiazepine (an anxiety medication), empty kitchen trash bags with plastic tape attached, vinyl tubing and medical cups with “white residue” were all discovered in the home. “In terms of the least amount of discomfort involved…a depressant medication would be useful in that it would slow the respiratory system down significantly,” Belcher said of a potential cause of death. He added that the plastic bags then "could have been utilized" around the upper body or head "in concert" with the helium gas. "That would (result in) significantly less pain than what might be accomplished by other means," he said.

Investigators are still awaiting the outcome of toxicology reports to officially confirm how Jeffrey and the children died, a process that could take several weeks, said Belcher.

The prescription medications, flowers and helium canister – rented by Tamisha – were all obtained on August 11, the day of the deaths, according to Belcher. “It certainly implies there was a thought process that went into what took place,” he said. “It seems evident to me...that some pre-meditation took place. Whether both parents participated in this remains yet to be discovered."

Belcher said it was “unclear” in what order the deaths of the family members occurred outside of Tamisha. “We may never truly know what the sequence of events was that unfolded in the house,” he said. Belcher said there was “no sign of a struggle” amongst any of the family members. A “very brief” note in Jeffrey’s handwriting found in the home contained a reference to the “children’s innocence in this circumstance,” Belcher said. He did not elaborate further on the note’s contents.

Jeffrey also called a relative on August 11 and left a message stating that two pets had died in the home. It was the last known contact with anyone outside the Mendenhall family. Belcher, who could not confirm what type of animals the family owned, said a forensic analysis was being conducted on the pets to discover whether their method of death was similar to that of family members.

Belcher called the tragedy a “horrible set of circumstances” and said it raised questions of whether anything could have been done to avoid the deaths. Grand Traverse Sheriff’s Office records indicate authorities had previously responded to suicide threats at the home made by both Jeffrey (in 2008 and 2012) and Tamisha (in 2013). Belcher did not know whether Child Protective Services had ever investigated the residence. He said it was "difficult to say what was on the minds of the parents."

“It’s a terrible, terrible thing for the entire community,” Belcher said. “It makes you wonder what could have been done differently by a number of different people. Could anything have been accomplished...had a slightly different sequence of events unfolded, could we have prevented this?" Attempting to answer those questions in the coming weeks, said Belcher, was crucial to ensuring that "as a community, we don't have to talk about something like this again."

Pictured above: Tamisha Mendenhall