It was hypothetical till post #5, when the facts were posted.
I understand the question is hypothetical. So give the information to L/P hypothetically and allow them to check it out.
I'm sure LP has a protocol to follow to see if a full investigation is required. If they can not find anything that warrants a full investigation, then no harm done. If the investigation is warranted, then they will act upon it.
I really doubt that L/P would investigate every single time one employee THINKS another employee is stealing.
If the driver has a illegitimate side business and was selling phones to his customers on his own time, then that information would come out. No harm done. Case closed.
If the driver has a illegitimate side business and selling while on UPS time, that I'm sure is against policy. What would happen if the driver was found guilty of stealing UPS time? Perhaps they would get written up and get a meeting with the shop steward, right? The Union would back the driver and UPS would paid for the grievance filed by the driver.
However, if the driver is indeed stealing merchandise from UPS packages, they need to be terminated, without a doubt. The only way that can happen is through L/P.
Personally, I would only discuss the information with L/P, that way the information remains confidential and not all over the package center.