While Sharlene was an eyewitness to DM and MS getting in the truck just before TB was killed, she testified she was unable to positively identify either accused; she gave general descriptions, mostly of DM, and said she didn't get a good look at MS, because he was wearing a red hoodie that covered most of his face; she described him as "sketchy." You may be thinking of the agreed-upon statement of fact that MS admitted to being a passenger when IT took them for a test drive the day before. IT *did* positively identify MS from a photo lineup.
As for someone's question about whether you can be convicted of M1 if you aren't physically there -- yes, you certainly can. In such convictions, the absentee killer is part of the planning and may even have arranged the homicide, or paid/convinced someone else to do it for him. Think back to the Peter Demeter case. He had an ironclad alibi for his wife's murder, but he had hired a hit man (who has never been found) and he got M1 . From prison he tried to arrange a few more hits on people who he had a grudge with! He will die in prison, where he has been for 40+ years.
We can't know what specific evidence convinced the jury in the TB case, as they are never allowed to reveal any content of their discussions. They can talk about their feelings, reactions etc. but nothing to do with their deliberations. Also,the different jurors don't need to agree on what the determinative evidence is, only on the verdict, which each may come to via a different path.