At about the 22 minute mark, Stella shows Mack a prescription they found in the alley. She mentions that they think it is a prescription "Carter" bought in the alley. However Carter isn't identified by name as a person of interest until several minutes later when Flack views video from an ATM.
Although some fluorescent lamps do use krypton, it could not be found in the glass from a broken bulb. Krypton is a colorless, odorless gas that is chemically very unreactive. It can be forced into forming compounds with fluorine, but only under laboratory conditions that are not present in a light bulb. If a bulb containing krypton were broken, the gas would simply dissipate into the surrounding air and not be present for laboratory analysis.
There is no way an athlete could hide a knee injury from the NFL. The NFL requires independent physical examinations at the combine or pro day.