[bsdimp]

Nobody! There were no copyright notices, and this is a work made before the US adopted the BERN convention. Prior copyright law required copyright notices.

We learned from the ATT vs Regents case that a judge ruled there was a large likelihood that AT&T couldn't establish it had a valid copyright on V32 because they never marked it properly.

[beefhash]

> Nobody! There were no copyright notices, and this is a work made before the US adopted the BERN convention. Prior copyright law required copyright notices.

...in the U.S.

This does not apply to other countries, especially continental European ones. They'll happily retroactively apply copyright for software, even when it wasn't explicitly protected by means of their jurisdiction claiming that software has is categorized as a work even before the convention. No license, no luck over there.

cf. https://virtuallyfun.com/wordpress/2018/11/26/why-bsd-os-is-...

If it's not deemed a work for hire (and given UNIX was a rogue operation at the time, that's not entirely unreasonable to question), then the copyright probably remains with Thompson and Ritchie themselves, or rather Thompson and Ritchie's family (or whichever way the inheritance process went). If it is, then probably Micro Focus via Attachmate via Novell via USL. Special considerations may also apply because it wasn't "published" in any sense of the world until past Ritchie's death.