It was bound to happen, and the timing was right for everyone.

That was the official take from Mayor Mitch Landrieu and departing New Orleans police Superintendent Ronal Serpas at a news conference Monday announcing Serpas’ retirement from the department and “from public service” after 34 years as a cop.

But there were signs of deepening disenchantment between the mayor and a man he once called his most pivotal hire when he plucked Serpas from the chief’s post in Nashville, Tenn., to return to New Orleans in May 2010 with a pedigree for police reform.

Serpas alluded to a new job he’s lined up that will let him stay in New Orleans. Loyola University announced late Monday that Serpas will join its criminal justice program.

Serpas taught classes for years at the university during his first tour at NOPD, and Loyola’s president, Rev. Kevin Wildes, sits on the Civil Service Commission, which has adjudicated many NOPD personnel issues and endorsed some significant changes requested by Serpas in the police command structure.

Landrieu voiced sanguine tones over the loss of Serpas, who sat at the helm of a trouble-plagued department over a rocky four years that included the net loss of more than 400 cops — nearly 30 percent of the force — and the imposition of federal consent decree mandating a litany of police reforms.

“It is with regret that we see you retire today,” Landrieu said. He added that “given where the chief is in his life and what his dreams are for his future and where the city is, this actually falls beautifully into the strategy to begin to develop the city for a new generation of leadership.”

The old generation of leadership, meanwhile, took a vague swipe at his critics. Serpas warned new interim chief Michael Harrison “not to get distracted by the sideshow barkers.”

Serpas touted the support of the mayor, “who I’ve enjoyed working with every single day.”

But relations may have been rockier than either man has let on. As rumors of Serpas’ departure frothed up over the past several months, so did indications that Landrieu had lost some faith in his police chief.

Amid calls by opponents for Serpas to go during Landrieu’s re-election campaign, the mayor sided with his police chief, but with little conviction, articulating no defense.

In June, during a nearly two-hour interview with The New Orleans Advocate, Landrieu held forth at length on a number of pressing issues. Then, when asked if he had confidence in Serpas, the mayor offered a simple, “Yes.” Next question.

Whether Serpas’ departure came on the business end of an ultimatum, a shove or even a suggestive nudge was unclear Monday.

But it was clear that the two were far from in lockstep.

Serpas has often been left alone to defend criticism from the City Council and others over the fallout from the loss of hundreds of officers from the force — largely the result of a four-year freeze on hiring that the Landrieu administration imposed to help patch a $100 million budget hole.

It was Serpas who faced the brunt of questions over police staffing levels following a June 29 shooting melee that killed one and injured nine others on Bourbon Street, while Landrieu publicly pressed Gov. Bobby Jindal to flood the city with state police. It hardly seemed like a tag-team effort.

“It seems as though there’s been a fairly chilly relationship with City Hall for a little while now. It seems like it’s been since last year,” said Donovan Livaccari, an attorney and spokesman for the local Fraternal Order of Police lodge.

Tulane criminologist Peter Scharf said there seemed to be an “odd relationship” between Serpas and the mayor, as well as a deepening rift.

“A lot of police officers were mad at Ronnie for this or that. But if you really look closely, there was some responsibility on the mayor as well,” Scharf said.

Other than a self-assessment on Monday, Serpas also has received scant credit for a recent decline in the city’s long-rampant murder rate from nation-leading levels.

Instead, Landrieu and others have touted the city-led NOLA for Life initiative, and a multi-agency approach to violence reduction that has a heavy federal component.

Michael Cowan of the New Orleans Crime Coalition said significant credit for the reduction should go to Serpas.

“I think NOPD was front and center on that,” said Cowan. “I would say he’s one of the top police leaders in the whole United States. That’s how he acted in the last four years.”

Cowan said he saw “a decent relationship” between Landrieu and Serpas. But others who know the two well say they rarely met in person, outside of occasional news conferences over high-profile violent crimes in the city.

They appeared together again, side by side, at Monday’s news conference, before a ceremony in which Serpas pinned the superintendent of police badge on the next man up.

Follow John Simerman on Twitter, @johnsimerman