LUBBOCK, Texas — Across from a sprawling cotton field, among mobile homes in varying states of decay, one stood out: a double-wide with a new, expansive metal garage and the only paved driveway on the dead-end street.

It was here that an unemployed former computer repairman with a bad back ran what a drug informant called the biggest fentanyl ring in Lubbock. All Sidney Lanier needed was a computer and an elementary knowledge of chemistry to order shipments of the potent synthetic opioid from China and turn it into a highly profitable — and dangerous — street drug.