David Herold's dog

[BettyO]

I think that the dog was brought into the prison, probably by one of Herold's sisters or friends for company. There is a report that Herold's sisters, during the trial, brought him fresh strawberries and crackers as a treat.

There is no report that Booth and Herold had a dog tagging along with them. Just the fact that the dog could bay and bring their pursuers closer would be a danger to the fugitives.