Sam Pinney, Samantha Simmons Busted in Double Murder: Pot Heist the Motive?

At first, the cause of death for Oklahoma's Joshua Foster and Zach Moore in northern Colorado last year appeared to be a vehicle fire.

But further investigation suggested that they'd been murdered, with the fire presumably set to cover up evidence of the crime.

And now, months after their passing, two people — Samuel Pinney and Samantha Simmons — have been arrested on suspicion of having killed them.

As seen in the photo above, Pinney sports a head tattoo that reads "Outlaw."

In addition, a third person, Nathaniel Young, is in custody in relation to the case. He's accused of playing a role in the robbery that precipitated the deadly chain of events.

The product thought to be at the center of the heist? Marijuana.

According to the Weld County Sheriff's Office, deputies received a call at around 10 p.m. on October 17, 2015 pertaining to a burning pickup truck.

The location: the intersection of Weld County Road 57 and Weld County Road 96 near the small community of Nunn.

The victims were subsequently identified as Foster and Moore.

Foster is seen in this photo from his obituary....

...which says he was the owner of a welding and towing service.

He was married and had a child, the notice reveals.

Meanwhile, the sheriff's office shared this photo of Moore.

Early on, investigators noticed suspicious circumstances surrounding the blaze that led them to surmise that something other than a traffic mishap may have been involved

Autopsy results confirmed this theory.

Analysis showed that Foster and Moore were dead before the fire was set, with the WCSO adding that "there was evidence suggestive of a gunshot wound to the head."

Moreover, a shell casing was found in the truck.

That left the question of motive.

And after further investigation, the WCSO notes, detectives "learned from sources that Foster had gone to Colorado on at least three other occasions in an attempt to purchase large quantities of marijuana to sell in Oklahoma."

Thus far, the sheriff's office isn't sharing details about how investigators used this information to tie Pinney and Simmons to the killings, other than the belief that "the victims were ambushed, robbed and killed."

Then, at 4:30 a.m. today, April 18, the Weld County SWAT team showed up at a residence on the 1200 block of Moore Drive in Gilcrest, Colorado, to serve what's described as a "high risk felony warrant" on Pinney and Simmons.

They're being held on suspicion of conspiracy to commit aggravated robbery, aggravated robbery, two counts of first-degree murder, another two counts of murder after deliberation, second-degree arson, criminal mischief and two abuse-of-a-corpse counts.

Additionally, Youngman is looking at a likely charge of conspiracy to commit aggravated robbery.

The sheriff's office points out that the investigation is ongoing. If you have information about what went down, you're encouraged to contact the tip line at 970-304-6464 x2861.

Look below to see booking photos for Simmons, Youngman and Pinney.