From narrative films (“Zodiac”), Tv series (“Mindhunter”) to doc series (see everything Netflix is consumed with and their Ted Bundy doc), serial killers tend to be compelling subject matter for crime thrillers. And thus, yet another new film gestating at 20th Century Studios will spotlight the notorious true-life Boston serial killer with Matt Ruskin (“Crown Heights”) writing and directing “Boston Strangler” starring Oscar-nominee Kiera Knightley, according to Deadline.