Scenario:

A police officer arrests a suspect for a controlled substance offense and the vehicle he was driving is impounded. The suspect is now in jail and the vehicle has been taken by the wrecker service to the storage facility. Can the officer go back to the storage unit and search (or do a more thorough inventory) the vehicle again without a warrant?

Same Scenario, but, a jailer contacts the arresting officer and reports he heard the suspect over a recorded line at the jail ask his friend to go to the car and "get his stuff." Pretty vague but it could lead the officer to believe some contraband was missed during the search and inventory.

Any case law to back the answers to these questions would be appreciated.

The ability to search the car doesn't change over time. If the officer had a basis for an inventory and wants to do it better, that's OK. If the officer had probable cause and wants to re-search, that's OK. If the officer develops late probable cause, that's OK.

You never need a search warrant for a car, unless you want to search it while it is parked in a place that is private (like the garage of the owner). All you need is probable cause or a another exeception (such as conducting an inventory). Of course, it wouldn't hurt to run a drug dog around the car before doing that second search based on jail phone call tip.

For cases, I recommend Tom and Ted's warrant book and Beckham's warrantless book.

It is amazing to me how many times we get a phone call from cops wanting a warrant to search a car.