I was inspired to write a big post and even record a video for this prompt, but pesky health problems have stolen my spoons whilst I was half way through; I’ll return to it after this event. Meanwhile, here are some links I gave to someone asking for investigation mechanics assistance.
Whilst not relating to mechanics, I also recommend checking out GURPS Mysteries. Many GURPS books are well written and this book I think is exceptionally well put together, providing a great exploration of the topic.
Years ago I persuaded some players that played lots of Call of Cthulhu to give SFRPG a go by highlighting how a core part of the game is about investigation; fortunately they enjoyed the games I ran. If veteran Investigators find SFRPG to fulfil their investigation needs, it shows the system does not need things, but like with many old games I have been pondering of adding mechanics from newer games to it. In this case using the Hunt Rolls from Trophy RPG, but I have not gotten to playtest this yet, but I will get to playtest it when I run my Game of Death fused with Twin Peaks adventure I am working on; day 19.
Other Peoples’ Answers
Anthony Boyd @Runeslinger
Charles Etheridge-Nunn @charlie_en
Sue Savage @SavageSpiel
Craig Oxbrow @CraigOxbrow
Heather Fey @slapjellyfish
Adam Dickstein @alien_barking
Bob Freeman @OccultDetective
Geek-Life Balance @cybogoblin
John M. Kahane @jkahane1
This is a non-exhaustive list; I still have many posts to read today, so I might be adding more links. I’d recommend searching the hashtag and judge those great answers for yourself: #RPGaDay2020, some people use #RPGaDay.