Boston ( CNN ) -- Jurors squirmed Monday as a Massachusetts pathologist detailed the wounds inflicted on the 19 bodies prosecutors have lain at the feet of reputed Boston mob boss James `` Whitey '' Bulger . Richard John Evans , the state 's former chief medical examiner , described gunshot wounds to the temple , neck , spinal cord or heart in graphic detail . The jury in Bulger 's federal racketeering and murder trial was both riveted and visibly uneasy during Evans ' testimony , with some of them holding their hands over their mouths as he outlined the damage inflicted by bullets in 17 of the 19 cases . Others twisted in their chairs during the testimony , while many intently took notes . But about eight victims into the litany of death certificates , the jurors appeared more relaxed . Most of the victims were shot repeatedly in the head or neck , Evans testified . They included William O'Brien , who was expecting a baby boy when he was shot 20 times on a Boston boulevard in 1973 . `` The most significant of the 20 was a wound to his right shoulder which pierced the spinal cord and lodged in his neck region , '' Evans explained . `` It severed the spinal cord five centimeters from the bottom of the brain stem , which would make breathing impossible . '' Former drug dealers detail threats during Bulger 's reign . Former gang associate Francis `` Buddy '' Leonard was found in 1975 riddled with 13 bullets , including two to the left side of the head and one in the neck , according to his death certificate . Another victim , Brian Halloran , was shot 14 times in 1975 . All of the shots were `` through-and-throughs , '' leaving no with bullets passing completely through the body , Evans testified . Dead alongside him was Michael Donahue , Evans testified , a friend who was n't affiliated with Boston 's criminal gangs . Donahue was giving Halloran a ride home from a bar ; his cause of death was `` a gunshot wound to back of head that went into his brain , '' Evans explained . Donahue 's son , Tommy Donahue , sat with his head in his hands and his eyes closed during the description of the shot that killed his father . `` Going through it was rough , but I know every word on that death certificate , '' Donahue said after Monday 's testimony . He brandished the document , which he has carried to court every day since the beginning of the trial , as he spoke . Prosecutors say Bulger had a nearly 20-year reign of terror as the head of the Winter Hill Gang , the Irish mob that once terrorized South Boston . But during much of that time , they say , he was an FBI informant , and that rogue FBI agents tipped him off to his impending arrest and allowed him to flee a 1995 indictment . Juror view photos of alleged victims ' remains . Now 83 , Bulger was captured in California in 2011 and brought back to Boston for trial , where a succession of mob figures have tied him to the killings . Former FBI Agent Gerald Montanari testified Monday that Halloran was a `` mid-level strong arm '' who had agreed to wear a listening device and testify against Bulger and his associates . He was protected by the FBI and stationed in a safe house on Cape Cod until he began to `` waffle '' about entering into the witness protection program and refused a polygraph , Montanari said . Montanari said the FBI cut ties with Halloran in 1982 . The mobster was found shot to death shortly afterward , and earlier testimony stated that Bulger had Halloran killed after his FBI handler tipped him off to Halloran 's cooperation . Former hit man John Martorano -- now the government 's star witness -- recounted Bulger 's involvement in 13 killings , including O'Brien 's and Leonard 's . Former associate Kevin Weeks implicated Bulger in three more , including that of Halloran -- whose body was `` bouncing off the ground '' with every shot , he testified . Prosecutors expect testimony later this week from Bulger 's former partner and fellow informant Stephen `` The Rifleman '' Flemmi to lock up their case . Weeks , Flemmi and Martorano have all testified in exchange for reduced sentences in other murders . Expletives fly Bulger , ex-partner during trial . CNN 's Laura Batchelor and Deborah Feyerick contributed to this report .
Medical examiner lays out fatal ##ity in Bulger case . Of the 19 killings Bulger is charged with , 17 were killed by gunfire . Some jurors cry during the graphic scene .