The crime has to be committed in connection with another violent crime, like robbery. Drewry knew robbery would be difficult for the commonwealth to prove, although Venable's girlfriend was a credible witness for the prosecution. But the death penalty also requires that the murder involve aggravated battery or future dangerousness. Aggravated battery means multiple gunshots or a particularly violent killing. The courts have ruled that one gunshot does not usually meet that test.
Future dangerousness is proved largely by past record.
While Venable had a juvenile record, there was some question it could be introduced because of a recent state Supreme Court ruling that both parents be notified of juvenile proceedings. Venable's father had not been notified, so Drewry believed it was unlikely the commonwealth could introduce that record. Still, Drewry had to prepare the case as though it would be a death case. I looked for weaknesses in their case first. It's still their burden of proof.