The old BSD wasn't freely licensed, though. Some versions included source code, but with no license permitting distribution of derived works.
The first even partial release of a free-software BSD was in 1989, when UC Berkeley first wrote the 4-clause BSD license (with the now-dropped "advertising clause"), and released a non-functioning OS core consisting of TCP/IP stack and libraries, called "Net/1", but couldn't release a functioning OS because they couldn't get permission to release the code that AT&T owned. They rewrote a bunch of the AT&T code as free software and released the first-ever free BSD, Net/2, in 1991, which then led to the 386BSD port, and thence to FreeBSD.
The first even partial release of a free-software BSD was in 1989, when UC Berkeley first wrote the 4-clause BSD license (with the now-dropped "advertising clause"), and released a non-functioning OS core consisting of TCP/IP stack and libraries, called "Net/1", but couldn't release a functioning OS because they couldn't get permission to release the code that AT&T owned. They rewrote a bunch of the AT&T code as free software and released the first-ever free BSD, Net/2, in 1991, which then led to the 386BSD port, and thence to FreeBSD.