It Came from the Desert/Evidence

The objects required to acquire evidence

Ant Fluid
Jackie's car on Day 2, Neptune Hall on Day 7, Quarry, and sometimes after fighting ants

Piece of Ant
Ben brings you one on Day 3, and sometimes you find after fighting ants.

Plaster Cast of Track
At the SW Cone on Day 4 (Geez will also drop one off at the lab), at Cook's Stud Farm on Day 7, or the mines

Tape Recording
Sometimes the miners can give you one, the Sheriff will give you one on Day 4, and Louie on Day 7. When Louie tells you that he has had the planes upgraded with recording machines, you can fly to SW and head back.