Activated carbon does absorb lead because it has a variety of binding sites that will bind to lead ions. The problem is, those binding sites are limited and will get quickly used up if you’re having to actually deal with any significant amount of lead and if you have other metal ions (like copper) trying to compete for binding sites the whole profile looks worse. This means if you’ve got hard water with a ton of competing ions, the filter will likely do dick for lead. So the Brita filters do do something, but if there’s an actual utility to what they do in regards to heavy metals depends on the water.
Witnesses need to introduce the evidence as to where they got it, where it was recorded, and how it was recorded, and if it was edited or it’s hearsay and inadmissible. These are common law evidence rules that are older than modern police forces and predate either pictures or video to where you were arguing about a tally stick contact. That said, the cops only want to be the sole depondent for citation level crimes usually so they’ve decided they don’t want to do the legwork of getting the person who recorded it to be the witness. They just don’t want to do the work. They’ll come up with reasons for that, but that’s the core.