The FBI should always be able to release documents when it is pertinent and necessary, and after careful investigation and unanimous decision-making within the organization. However, releasing documents with little or no relevance in a way that creates suspicion about a candidate so close to an election is highly irresponsible and reprehensible.
The FBIs job is to investigate crime in the US. If Hillary clinton has commited a crime, then it is the FBIs job and duty to investigate and expose it, no matter how close to the election it is.
FBI director James Comey would have gotten slammed by the republicans anyway if he left the reopening of the investigation till after the election.
It is their work so safe guard the interest of people and the nation at large. Their duty is to secure not only the government information and infrastructure, but to also put check point at every situation that concern the safety of the citizen of US. Bring the issue of Clinton handling of private email, go a long way to tell the America people that being a politician doesn't make you not in a watch-list of FBI investigation. No one is above the law.
The FBI should be allowed to report on their conclusions in cases but to offer up information on open cases is not necessary. They more or less said they went public to not be called out later. The FBI was in a cant win situation and were seen as favoring the Clintons so this is a strategic route to balance.
The decision by the FBI to revisit the investigations of the two leading Presidential candidates is ill-timed and ill-advised. In some countries, candidates seeking the highest office in the land do have to undergo rigorous screenings by security agents before they get any green light.
If the FBI goes ahead with the investigations and release increminating documents about any candidate at this time, it would clearly confirm the allegations by many, that the organisation is already biased towards a particular candidate.