Legally, yes, they could have been hanged. Would it have been “just?” That’s a matter of subjective opinion. My personal opinion is that, in the interests of healing the wounds and reuniting the nation, it was best to not hang them.
That is really rich. The US Government feared losing a treason trial so they let Davis go. Davis spent time in Canada and Europe after the war and voluntarily returned several times DEMANDING a trial which the sniveling cowardice US government failed to do. Davis would have won and the consensus at the time was that a trial would be a disaster for the US Govt.
There was a great deal of discussion in 1865 about bringing treason trials, especially against Jefferson Davis, and there was no consensus in President Johnson's cabinet to do so. There were no treason trials against anyone, as it was felt they would probably not succeed and would impede reconciliation.[140][141][142][143] After two years of imprisonment, Davis was released on bail of $100,000, which was posted by prominent citizens including Horace Greeley, Cornelius Vanderbilt and Gerrit Smith.[144]