Officially Thomas Baron's death is ruled a suicide. Had he been murdered, it would have made more sense to do that before he testified and before he delivered a lengthy report to Congress. Baron had already been known to the press as a sort of whistle-blower and a critic of North American since early 1967 at the latest. To try to "silence" him three months later, after his testimony, is useless.
NASA had nothing to gain by Baron's death. North American would have had something to gain had it occurred before his testimony and report. As it happens, North American was not seriously implicated by Baron's testimony. NAA was able to substantiate that it had acted on the valid points of Baron's first report with due diligence, and was doing so when the Apollo 1 tragedy occurred.