Most accounts of Heaven's Gate begin in March 1997. The most useful evidence about it was gathered in 1975, when the sociologists Robert Balch and David Taylor joined the group covertly and travelled with it for two months.
What they found cuts against the picture that would dominate the coverage twenty two years later. There was no coercion to speak of, no isolation compound and no pressure to stay. Members were recruited at public meetings advertised in local newspapers, and Balch and Taylor watched the great majority of recruits leave within weeks under their own power. The commitment that held the remainder was, in their reading, less a matter of anything done to people than of what people brought with them: most were already seekers who had passed through several movements, and the group offered a framework that made sense of a search begun elsewhere.
Balch continued to follow the group and its former members for the next two decades, which makes Heaven's Gate one of very few new religious movements with a longitudinal record predating its notoriety. That record is why claims that the 1997 deaths were the product of sudden manipulation are hard to sustain. The theology of the body as a vehicle, the Next Level, and the expectation of a bodily departure were all in place and being taught publicly in 1975.
The group's own material survives as well, because former members have maintained its website continuously since the deaths, answering correspondence and declining to reinterpret the teaching for later readers.