No. The priest cannot. Although the penitent is permitted.
The penitent can request that the priest talk about it outside of Confession, but that doesn’t always mean that the priest will, or that he will even remember.
Or what about if a killer who confessed decides to give himself up to the police, can he request the priest to cooperate with the police regarding information?
He can request anything. That doesn’t mean it will happen.
The penitent can release the priest from the Seal, but the priest is also protected by the Seal. The priest would have to be absolutely certain that the penitent made this decision without any coercion whatsoever (which is very unlikely), and would also have to freely decide to do this (which is even more unlikely). In the case of someone accused of a crime, it’s almost impossible for those standards to be met. If there is even the slightest hesitation or doubt about either party, the Seal remains.
If we’re talking about someone accused (or convicted) of a crime, the likelihood that the priest would be genuinely convinced that the penitent is acting without any coercion whatsoever is so near-impossible that no priest would really accept the claim that the penitent is acting freely. Even if he does, the priest is still protected by the Seal, and it’s not likely he would be willing to surrender his own right to keep the Seal.
The penitent is free to say anything, of course. No one is prohibited from saying something like “I went to confession yesterday, confessed XYZ, and I’m so glad I did.” That’s not a problem.
The only time something like this can happen would be more “everyday” types of situations. It’s not unusual for people to say something like “I missed Mass last Sunday, then I went to Confession.” OK fine. Not a problem. But still, the priest is bound to simply not say anything.