That surveillance cameras are everywhere these days is either good or bad, dependingon whom you talk to. Cops like the ubiquity, civil libertarians not so much. But their value in solving crimes is not debatable, as the Investigation Discovery series “See No Evil’’ makes clear. The popular show uses real closed-circuit television footage to explain how villainy is revealed, and it’s often terrifying. Tuesday’s episode focuses on the 2013 murder of Amy Lord, whose abduction was captured by surveillance cameras all over Southie. (Her killer, Edwin Alemany, was convicted and sentenced to life in prison.) It includes interviews with Lord’s sister, Carly, prosecutor John Pappas, Boston Police detectives, and Kayleigh Ballantyne, who was attacked by Alemany in the hours after Lord’s death.