Inspired by actual events, “Blue Caprice” hews so closely to the Beltway-snipers case of 2002 that it almost qualifies as a docudrama. But this low-key thriller has been fictionalized, for no apparent reason.

Director Alexandre Moors and co-writer R.F.I. Porto favor a more oblique psychological angle on the snipers, who randomly killed 10 and wounded three during a 23-day spree in Washington, D.C., and Virginia. (The film’s title refers to the 1990 Chevy they modified into a nondescript sniper’s nest.)

Ex-convict John Allen Muhammad and his teen accomplice Lee Boyd Malvo had local ties before their rampage: Muhammad rescued the abandoned teen in Antigua, then returned to his Tacoma home with Malvo as a surrogate son. A twisted mentorship ensued, fueled by Muhammad’s urge to kill his estranged wife, who’d filed a restraining order to protect herself and their children. His quest for revenge took them cross-country to Maryland.

Muhammad and Malvo are played, respectively, by Isaiah Washington and Tequan Richmond; to the extent that their characters are developed, both performances are superb. Washington shifts from father figure to sociopath with disturbing subtlety, and Richmond is scarily convincing as an eager student of Muhammad’s combat training. Tim Blake Nelson is similarly unnerving as a gun lover who arms them, and Joey Lauren Adams makes the most of fleeting scenes as his frazzled, weary wife.

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It’s the movie’s vague intentions that ultimately render it inert. If Moors and Porto were aiming for gun-debate relevance, they’ve failed; “Blue Caprice” has nothing to say about a society plagued by violence, nor does it focus on mental illness as a probable cause. With conspicuous art-house style, “Blue Caprice” is instead a thinly drawn portrait of a needy kid blindly devoted to the man who, ironically, gives him a second chance before tragically breaking bad.