Cranks does not start

This could be a number of things but we are going to have to do some testing.

Here is a video that covers some basic things to start with:

https://youtu.be/dCjmRL3p4Cs

Your engine needs three things to start and run. Spark, fuel, and compression. So we need to start with fuel. Let's check the fuel pressure and see what that says. Here is a guide that shows how to do that:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Another way to do this is just spray some starting fluid in the intake and see if the engine starts briefly. If it does then we have a fuel issue. Then we will need to do a fuel pressure test.

Lastly here is another guide that will help with what is happening and it covers an engine that cranks but does not start:

https://www.2carpros.com/articles/car-cranks-but-wont-start

As for the mechanic not knowing what was wrong because it did not connect to his tool, sounds like you need a second opinion. If he stopped after that then I am not sure how knowledgeable they are just because that could be a scan tool issue, an issue with the ECM that could be causing this issue, or not related at all.

Let us know what questions you have. Thanks