The inquest on Kelly ended at ,for arguments sake, Monday 2-4 pm,based on the number of questions asked of witnesses and
depending on how long the witness recited his/her testimony,Hutch came at 6:00 pm.
It's safe to assume the reason Hutch came forward was because the inquest ended abruptly.there were no more inquests.
He then did not have to face the jury,coroner,etc in an inquest court where his testimony was under oath,and was liable
for contempt/fine if caught lying.
In the police station he was not in the same oath and could retract his statement,for ex.
mixing up the days and end up released like witnesses who reported suspicious men who could be the ripper.Besides
Astrakhan man was not present and Hutch was not "accusing/perjuring" somebody which,I assume ,was another/or additional offense.
All he had to know was in a court, as opposed to a police station,testimonies were formal,subject to fine/contempt if lying.
Before 1911 Perjury Act, perjury was confined to the courts (Perjury Act 1728).
Coroners act 1887
The coroner, being guided by
the information he has received, usually sends a message
to those witnesses whom he thinks material. Should
they neglect or refuse to attend, the coroner, as incident
to his office of judge of a court of record, has authority
to issue a summons to compel their appearance where
he has been credibly informed that they are able to give
evidence, and he may if necessary issue a summons to
the constable to bring them into court. If a witness
refuses without sufficient reason to obey this summons,
the coroner may fine him £2 under section 19 ; and if a
witness refuses to give evidence when sworn, or otherwise
misconducts himself in court, the coroner has power to
commit him for contempt. The coroner has also power
to issue a warrant against a witness for contempt of the
summons, under which the constable may bring up the
witness in custody.
Above, to me, the reason Hutch came forward.
Clearly the first human laws (way older and already established) spawned organized religion's morality - from which it's writers only copied,ex. you cannot kill,steal (forced, otherwise people run back to the hills).