PITTSFIELD — Prosecutors say a Massachusetts man fatally shot his ex-girlfriend during an argument when she came to his home to pick up their children.Michael Boulais was held without bail after pleading not guilty Tuesday in district court in Pittsfield to a murder charge in the death last week of Kassedi Clark.Authorities say the 32-year-old Boulais shot the 24-year-old Clark multiple times with a 9 mm handgun in her car when she came to his Hinsdale home on Friday.