AT&T apparently "stole" and "pirated" it from those communists at MIT who were working on Multics, just like Excel was stolen and pirated from Visicalc which also came from the greater communistic MIT community.
"Over time, hope was replaced by frustration as the group effort initially failed to produce an economically useful system. Bell Labs withdrew from the effort in 1969 but a small band of users at Bell Labs Computing Science Research Center in Murray Hill -- Ken Thompson, Dennis Ritchie, Doug McIlroy, and J. F. Ossanna -- continued to seek the Holy Grail." -- Lucent web page
"... the problem was the increasing obviousness of the failure of Multics to deliver promptly any sort of usable system, let alone the panacea envisioned earlier." -- Dennis Ritchie, "The Evolution of the Unix Time-sharing System"