Kevin Lino. Handout/DAs Office

A man currently serving time for killings in Montana and Boston is now facing two additional murder charges in separate cases in Lowell and Cambridge, authorities said.

A Middlesex County grand jury on Tuesday indicted Kevin J. Lino, 38, on two counts of first-degree murder in the deaths of Gary A. Melanson, who was killed in November 2010 in Lowell, and Douglas Leon Clarke, slain in Cambridge in August 2012, District Attorney Marian T. Ryan said Tuesday at a news conference.

“Obviously, these allegations demonstrate a very violent pattern of behavior, [with prosecutors] alleging a targeting of some of the most vulnerable members in the community,” Ryan said.

A lawyer for Lino declined to comment.

One challenge for investigators was that the manners of

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