The dispute over the release of the Jacob Wetterling investigative file grew more complicated Tuesday when the U.S. Department of Justice filed a civil complaint with Stearns County demanding that it return all of the FBI's documents in the case.

The 10-page complaint was signed by Greg Brooker, the U.S. Attorney for Minnesota.

The move to intervene in the case and reclaim possession of the documents will almost certainly extend court proceedings and further delay the release of any of the files, which should shed light on the inner workings of an abduction investigation that gripped a state and region for 27 years.

The case file, which contains some 10,000 documents and 56,000 pages of information, was set to be released by Stearns County in June until Patty and Jerry Wetterling, Jacob's parents, sought to stop it in hopes of keeping 168 pages permanently sealed on the grounds that they're overly intrusive.

It is estimated that well over half the documents in the file originated with the FBI.

In the complaint filed Tuesday, Brooker argued that the FBI documents were merely on loan to Stearns County law enforcement and should now be returned, rather than released.

Whoever controls the documents determines whether they are released and when.

Under Minnesota law, the presumption is that the documents are public unless an exception is proven. Under federal law, obstacles to public access are much greater.

"This is going to make a substantial difference to the Wetterlings," Doug Kelley, the Wetterling's attorney, said about the FBI's attempt to take back its documents. If they are returned, it is much more likely the Wetterlings will succeed in their bid to keep them private, Kelley said.

Attorney Mark Anfinson, representing media and watchdog groups that are pushing to open the entire file, said Tuesday's filing by the federal government would "heighten the drama and reduce the efficiency of this litigation."

Almost three decades of mystery over Jacob's wrenching October 1989 disappearance ended in 2016 when Danny Heinrich, a former Paynesville, Minn., resident, acknowledged abducting the 11-year-old at gunpoint on a rural road near the boy's St. Joseph home and killing him. Heinrich led authorities to the boy's remains in a pasture near Paynesville.

Under Minnesota law, once a case is closed, the investigative file is opened to the public. As crime victims, however, the Wetterlings were allowed to read the file before it was released.

Days before the Stearns County Sheriff's Department was set to open the file to the public, the Wetterlings filed suit seeking to block its release.

Last fall, District Judge Ann Carrott allowed a coalition of open government, public interest and media organizations to intervene in the case. The organizations have argued that the entire file should be public.

Don Gemberling, speaking on behalf of the coalition, agreed with Kelley, saying that if the federal government controls release of the documents, they are likely to remain sealed.

"We'll never know, for example, in an investigation that most people believe was fundamentally flawed, who screwed up," Gemberling said.

Heinrich, for example, was questioned and released within six weeks of Wetterling's disappearance.

Being able to see the file would be "an interesting opportunity in a case that consumed tons and tons of resources and went on for a really long time," Gemberling said.

While the FBI was involved in the search for the boy, Stearns County, where Jacob was abducted and killed, was the lead investigative agency.

Earlier this year, the FBI appealed to Stearns County Sheriff Don Gudmundson and Stearns County Attorney Janelle Kendall in hopes of reclaiming the documents. Both denied the FBI's requests.

If Carrott grants the federal request to intervene in the case, she must then determine whether the documents should be returned to the FBI. Kelley said most of the documents of concern to the Wetterlings are FBI records.

The group represented by Anfinson includes the Minnesota Coalition on Government Information, the Silha Center for the Study of Media Ethics and Law, the Minnesota chapter of the Society of Professional Journalists, and the state newspaper and broadcasters associations, along with KSTP-TV, WDIO-TV, KAAL-TV, Minnesota Public Radio and the St. Paul Pioneer Press.

The Star Tribune is a member of the Minnesota Newspaper Association.

A conference call between Carrott and attorneys to discuss the status of the case file is planned for Wednesday with the expectation that a revised schedule for addressing the issue will be set.

Twitter: @rochelleolson