It is a defense strategy to give the jury an alternative suspect and involves more than simply throwing a name out there. It can involve an alternative senario, motives the defendant lacks, revenge, a bad business deal, stalker, drug involvement, poking holes in the police investigation:
evidence can include evidence that the police inadequately investigated alternate suspects
or that they had "tunnel vision" and failed to pursue important lines of inquiry.
Of course they don't have to offer the jury anything, they can just let the jury decide for themselves who could have possibly done it if it wasn't the defendant. If it wasn't the defendant someone else had to have done it.
Juries respond better when they have other possible alternative suspects.
There were other POI's in this case. For example:
The hoodie guy at food truck that Maddie told "eff you."
How does a criminal defense attorney argue for a Not Guilty verdict? One strategy is simply to argue that the state’s case is incomplete and has not been proven beyond a reasonable doubt; no more is required. Another strategy is to provide alternative explanations of each piece of evidence...