I know almost nothing about this case, but from the bare-bones description in TFA saying that two juries believed Glossip was part of a "murder for hire" scheme, I'd say that there are lots of places where the testimony should be verifiable:

* Does the murderer get any benefit from identifying this
guy (reduced sentence, etc.)?
* Does the murderer have any motive? That article
implies that robbery was the motive, this could be
substantiated by looking at what he took, how much it
was worth, and whether he'd have any reason to target
this guy otherwise. For example whether he ignored any
obviously better targets of opportunity to get this
specific person.
* Did the murderer know things about why Glossip
allegedly wanted this guy dead that he couldn't
reasonably have known otherwise?
* This was allegedly murder for hire: did Glossip give
this man any large amounts of money and if he did, was
there any other explanation? Has he given out large
amounts of cash before?
* Does the murderer have any psychiatric or drug-induced
conditions that make him see things that aren't there?
* Are there any provable lies in either person's story or
any history of lying to investigators in the past? If
so, are the lies better explained by confusion or
self-protection?
* Did Glossip ever know things he shouldn't have known
about the murder?

I do not claim to know the truth of any of the above statements, mind you. It's very possible that the answers exonerate Glossip, but the story should be something that can be corroborated and verified. There are lots of facts implied by the story which can be substantiated (or disproved) with sufficient investigation. So it shouldn't be the case that we just don't know--the facts will tell a story if the questions above are carefully investigated.

That said, I would think that they really shouldn't go for the death penalty if they don't have direct evidence, that just seems like too much. But they could, in theory, have answers to the above that eliminate reasonable doubts about his guilt, or lack thereof.

That aside, I am wary of the techie bias of ignoring motives entirely and looking only at physical evidence. Death Note, of all things, illustrates the difference the best, with Light always taking pains to produce no physical evidence, while L counters this with deep insight into his motives. We saw a lot of that with Reiser, as I recall.

In the end, though, I lack sufficient data to claim to have any reasonable idea about whether Glossip is innocent or guilty. All I'm saying here is that it shouldn't be the case that it's somehow unknowable or unverifiable given enough investigation into the questions posed above.

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EDIT: Another comment pointed to this: http://www.ca10.uscourts.gov/opinions/10/10-6244.pdf

I can see lots of places to corroborate (or disprove) the story -

> Sneed said that he and Glossip went to room 102 to make
sure Van Treese was dead.

This could have left physical evidence (or witnesses).

> He found an envelope with about $4000.00 cash under the seat. He came back and swept up the glass. He put the broken glass in room 102, just inside the door. He said that Glossip took the envelope from him and divided the money with him. He also testified that Glossip helped him put a shower curtain over the window, and he helped him cover Van Treese’s body.

There may be physical evidence left by this (or not), not to mention the money & envelope (fingerprints?).

> D-Anna Wood testified that she and Glossip were awakened at around 4:00 a.m. by Sneed. She testified that Glossip got out of bed and went to the front door. When he returned, Glossip told her that it was Sneed reporting that two drunks got into a fight and broke a window. She testified that Glossip then returned to bed.

This seems to say that Sneed is lying, unless D-Anna has some motive for protecting Glossip. Given that they're in bed together, and given the following, it's not implausible that she was protecting him.

> [Billye Hooper] asked Glossip about the car, and Glossip told her that Mr. Van Treese had left to get supplies for remodeling rooms.

This is highly suspicious.

> Cliff Everhart, who worked security for Mr. Van Treese in
exchange for a 1% ownership, was already at the motel. He told Sneed to check all of the rooms. Sneed indicated that he did so.

This is also really suspicious. He really should've known this guy was dead by then, but it really looks like he's avoiding it. And there are two people poking holes in his story.

> Subsequent searches revealed that Sneed possessed approximately $1,700.00 in cash, and that Glossip possessed
approximately $1,200.00. Glossip claimed this money came from his paycheck and proceeds from the sale of vending machines and his furniture

This corroborates Glossip's story, though we'd have to see if there was any merit to Sneed's alibi or not. One could look for physical evidence around the money, etc.