The closure makes Tucson the latest two-newspaper town to lose one of its dailies. The Citizen published in the afternoon while the Arizona Daily Star has appeared mornings. Both papers have a joint operating agreement.
The news prompted Attorney General Terry Goddard to file a motion for a temporary restraining order and a lawsuit alleging that the Citizen's closure violates state and federal antitrust laws.
"I believe serious questions must be answered about whether this action violates the antitrust laws," Goddard said in a statement.
In a phone interview, Goddard said he believes his office has a strong legal argument that what is being done isn't permissible under the antitrust laws. "And action would be taken to put the pieces back together," Goddard added.
It wasn't clear when U.S. District Judge Raner Collins could rule, but Goddard said he was told the judge wasn't available before Monday.
Kate Marymont, Gannett Co. vice president for news, said late Friday company lawyers were studying the documents filed by Goddard but declined further comment.
Earlier in the day, Marymont told the newspaper's staff that the Citizen will continue online with commentary and opinion but no news coverage. A printed Tucson Citizen editorial weekly will be distributed with the Star.
"Dramatic changes in our industry combined with the difficult economy ... means it is no longer viable to produce two daily printed newspapers in Tucson," said Bob Dickey, president of Gannett's U.S. Community Publishing Division.
Gannett, the largest newspaper publisher in the country, announced in January that it would close the Citizen if it didn't find a buyer for certain assets by March 21.
Four days before the planned closing, Gannett announced the Citizen would remain open while it negotiated with two interested buyers. Those talks ultimately proved unsuccessful.
"In the end, there were no buyers," Marymont told the Citizen staff.
Goddard's complaint said that Santa Monica Media Co. offered to pay Gannett either $250,000 immediately or $400,000 over time for Citizen assets. Gannett demanded a bid of $800,000 and broke off negotiations when the company declined, according to the filing.
Profits for Gannett and Lee's business partnership, Tucson Newspapers Inc., were $16.5 million in 2008 and its profit margins exceeded 19 percent.
The complaint said that Gannett and Lee Enterprises Inc., publisher of the morning Arizona Daily Star, were closing the Citizen to increase profits to both companies, and doing so would "substantially lessen competition."
The final issue of the Citizen will be a 40-page commemorative edition, with 25,000 to 30,000 copies printed and distributed to home subscribers, in vending machines and by street vendors, editor Jennifer Boice said.
On its Web site Friday, the Citizen feature a multimedia medley, from "Our Epitaph" written by Boice and photos of historic front pages to other staffers' memories and comments, video farewells and photo slideshows.
"I'm really sorry to see it go," Boice said. "We served a function in this community. We made other news media better."
During its lifetime, the Citizen reported on Arizona's biggest stories, including Marshall Wyatt Earp's fabled 1881 shootout at the OK Corral and the 1934 arrest of bank robber John Dillinger and three other gang members hiding out in Tucson.
But the Citizen has struggled for years against the Star, a 117,000-circulation newspaper. During the Citizen's heyday in the 1960s, circulation was about 60,000, but it had fallen to 17,000.
The Citizen becomes the latest casualty of a newspaper industry struggling to survive despite the economy, dwindling advertising revenues and Internet competition. The battle has been especially tough in two-newspaper towns like Tucson.