(Clackamas Co., OR)  --  Authorities say they've arrested a Milwaukie man who shot a woman to death and tried to shoot his ex-wife at a home in Clackamas County.  Sheriff's deputies say Gregory Siegberg was arrested Sunday night after being accused of killing 53-year-old Melissa Vargas at the house in the area of Southeast River Road and Southeast Torbank Road.  Siegberg is also accused of attempting to kill his former wife, Debra Kusch-Siegberg, who told deputies she was able to get out of the house and run to the home of a neighbor who called 911.  Gregory Siegberg, who was arrested in Ridgefield, Washington, was booked into the Clark County Jail on a DUII charge, and will soon be taken to Clackamas County, where he's expected to face charges of murder and attempted aggravated murder.