POCATELLO — Bannock County Prosecutor Steve Herzog says the knife used to kill an elderly Pocatello woman in March will likely never be found.

But he said the absence of the murder weapon will do nothing to weaken the prosecution's case against Dustin Garrett Alfaro, 18, of Marysville, California, and Isaac Angel Rodriguez-Romero, 17, also of Marysville, for allegedly stabbing to death 87-year-old Arlyne Koehler in her Pocatello home.

"We have a very solid case," Herzog said Wednesday. 

Authorities say Mrs. Koehler was stabbed more than 55 times on March 19 as she slept in the bedroom of the McKinley Avenue home where she lived alone. Family members found her body later on March 19 and contacted police.

Alfaro and Rodriguez-Romero have been charged with conspiring to kill her and then carrying out that murder with a knife.

Herzog said Alfaro told Pocatello police following his arrest that Rodriguez-Romero threw the knife from Alfaro's SUV as they drove back to Marysville, a city in Yuba County, California, after allegedly murdering Mrs. Koehler in Pocatello.

"The knife is somewhere between Pocatello and Yuba County, California," Herzog said in referencing Alfaro's statement to police. 

Herzog said authorities are not actively searching for the knife and they're also not sure whether the weapon was brought into Mrs. Koehler's home by the teens or if they acquired the knife from inside her home.

Herzog said the autopsy on Mrs. Koehler's body indicated that the knife possibly only had one sharp edge, similar to a pocketknife or kitchen knife rather than a knife with two sharp edges such as a dagger, but not much else is known about the weapon.  

One important piece of information that has been revealed by authorities this week is how Pocatello police found out that Alfaro and Rodriguez-Romero had allegedly murdered Mrs. Koehler. 

Prior to his arrest Alfaro had told a California woman he's acquainted with that he and Rodriquez-Romero had committed the murder, authorities said. This woman then contacted Pocatello police and that is what led to the two teenagers being arrested in California. 

Alfaro, following his arrest, threatened this woman via a phone call from jail for talking to Pocatello police, authorities said. 

Prosecutors have requested that the media not identify the woman because of fears for her safety. 

The court proceedings against Alfaro and Rodriguez-Romero continued this week at the Bannock County Courthouse in Pocatello.

Alfaro appeared before Judge Robert C. Naftz on Monday and pleaded not guilty to one count of principal to felony murder in the first-degree, one count of conspiracy to commit murder in the first-degree and a weapons enhancement charge for using a deadly weapon in the commission of a felony crime for Mrs. Koehler's death.

Rodriguez-Romero also appeared in front of Naftz on Monday but he declined to enter a plea to the charges he faces, which are identical to Alfaro’s charges.

Bannock County Deputy Prosecutor JaNiece Price told the Idaho State Journal that although Rodriguez-Romero did not enter a plea Monday, the court interprets his refusal as a not guilty plea.

Last week Judge Aaron N. Thompson ruled that Alfaro should stand trial for Mrs. Koehler's death following the teen's two-day preliminary hearing at the Bannock County Courthouse.

Rodriguez-Romero was scheduled to appear in court last Thursday and Friday for his preliminary hearing, but his Pocatello attorneys, Bradley Willis and Robert Otto Eldredge Jr., waived the hearing after Thompson on Wednesday ruled there was enough evidence to send Alfaro's case to trial. By waiving his preliminary hearing, Rodriguez-Romero's case will automatically be sent to trial. 

“We sat through all but 15 minutes of Alfaro’s preliminary hearing and we would not have had anything different to present for our client when Alfaro was bound over on all charges,” Eldredge Jr. told the Journal during a Tuesday phone interview. “We did not do it for strategic reasons."

Moreover, Eldredge Jr. said that Rodriguez-Romero did not enter a plea Monday because as a juvenile he was afraid to speak in court.

In deciding to send Alfaro's case to trial, Thompson relied heavily on two separate videos. One was Rodriguez-Romero videoing himself on his smartphone admitting to the murder less than 24 hours after it had been committed. The other was a Facebook video call between Alfaro and the aforementioned woman from California.

During the Facebook video call, Alfaro’s hands appeared bloody and he used gang terminology to admit to the murder.

Another piece of evidence presented during Alfaro’s preliminary hearing — video of an interrogation of Alfaro by Pocatello police detectives Richard Sampson and Niko Gordon — also played a role in Thompson’s decision to send Alfaro's case to trial.

Both Alfaro and Rodriguez-Romero were arrested on March 20 in Yuba County, California, for murdering Mrs. Koehler. Their arrests came less than 48 hours after Pocatello police held a press conference alerting the public that she had been murdered and that the suspects were still on the loose.

The teens were subsequently extradited to Idaho to face charges for the murder.

Alfaro was interrogated by Sampson and Gordon upon his arrival at the Bannock County Jail in Pocatello, where he remains incarcerated on a $1 million bond.

The detectives prefaced the interrogation with words of caution for Alfaro, with Sampson telling Alfaro that he had an opportunity to review phone calls Alfaro participated in while he was incarcerated at the Yuba County Jail in California awaiting his extradition.

The woman who spoke to Alfaro via Facebook video chat said that Alfaro called her from the Yuba County Jail and threatened her after hearing she had alerted Pocatello police.

Price told the Journal that Alfaro can be heard on the audio recording of the Yuba County Jail phone call demanding the woman recant what she told police and if she refused, he would have someone “wreck her home or belongings.”

Sampson and Gordon also questioned Alfaro about the weapon used to fatally stab Mrs. Koehler over 55 times. During the interrogation, Alfaro said he did not attack Mrs. Koehler, telling the police detectives it was Rodriguez-Romero who killed her using a large "kitchen knife.”

Alfaro told the police detectives he did not know if Rodriguez-Romero had the knife prior to entering Mrs. Koehler's home or if the knife was acquired from somewhere inside her home. Alfaro told the detectives he believes Rodriguez-Romero tossed the knife out of the window of Alfaro’s 1998 Ford Explorer as the pair fled back to California.

Alfaro also told the police dectives he burned his and Rodriguez-Romero's clothes after the pair arrived back in California following Mrs. Koehler's death.

Alfaro repeatedly told the police detectives that he and Rodriguez-Romero had picked Mrs. Koehler's house at random to burglarize because they believed it was vacant. Alfaro told the detectives that when Mrs. Koehler was found sleeping her bedroom it was Rodriguez-Romero that murdered her. 

Rodriguez-Romero, who is scheduled back in court for a status conference hearing in December, remains incarcerated on a $1 million bond at the 6th District Juvenile Detention Center in Pocatello. Because he was a juvenile at the time of the murder, U.S. Supreme Court case law says it is unconstitutional for him to face the death penalty. He still faces a maximum punishment of life in prison if convicted.

Alfaro, who is due back in court for a status conference hearing in November, faces a maximum punishment of up to life in prison or the death penalty if convicted of the charges against him. Prosecutors have not yet commented on whether they will pursue the death penalty against Alfaro.

Trial dates for Alfaro and Rodriguez-Romero have not yet been set. 

Reporter Shelbie Harris can be reached at 208-239-3525. Follow him on Twitter: @shelbietharris.