Chris Evans had little to say before or after Monday’s Boston Film Festival screening of “Stranglehold: In the Shadow of the Boston Strangler,” in which the studly Sudbury-bred actor does some voice work. (He reads the letters of the self-confessed strangler.) Evans was mostly mute on the red carpet prior to the screening and then opted not to take part in a post-screening Q&A at the Revere Hotel’s Theatre 1. The “Captain America” actor waved off questions so that his childhood friend, the film’s director Myles Jewell, could get all the attention. “Naw,” Evans said, when invited by moderator, “The Fighter” co-producer Keith Dorrington, to join the Q&A. “I’m not coming up there.” Though Evans spent most of the night slouched in his seat under a Bruins hat — a beer and Jewell by his side — he did hang around for the entire film and the chat afterward. Evans walked to the screening at Loews Boston Common from the apartment he owns in Chinatown, and afterward he quietly slipped out the back door alone.