Re: Any jurisdiction...
In England and Wales, this falls within the Defamation Act 2013.
The burden is on Rob to show - on the balance of probabilities - that Bob's statements on the billboards have caused "serious harm" to his reputation.
s.1(1) A statement is not defamatory unless its publication has caused
or is likely to cause serious harm to the reputation of the claimant.
There are 6 statutory defences available to Bob, but the ones that appear relevant to the OP are at s.2 and s.3 of the 2013 Act.
s.2(1) It is a defence to an action for defamation for the defendant
to show that the imputation conveyed by the statement complained of is
s.3(1)It is a defence to an action for defamation for the defendant to
show that the following conditions are met.
(2)The first condition is that the statement complained of was a
statement of opinion.
(3)The second condition is that the statement complained of indicated,
whether in general or specific terms, the basis of the opinion.
(4)The third condition is that an honest person could have held the
opinion on the basis of—
(a)any fact which existed at the time the statement complained of was
(b)anything asserted to be a fact in a privileged statement published
before the statement complained of.
If Bob has obtained "evidence sufficient to prove that beyond reasonable doubt" I cannot see how Rob's claim would succeed if Bob can prove the statements to be true.
NB there is no statute of limitations for theft in E&W, but it may not be in the public interest to prosecute for low value items so long after the offence.