Something about the way Maria Isabel Jaime reacted to being robbed at gunpoint struck her colleagues as strange.

Indeed, Jaime would later tell federal agents, she knew the man in the black ski mask who forced his way into the south Minneapolis TCF Bank branch as she and a co-worker opened one morning last fall.

It was her boyfriend, Felix Mendez.

Now the couple face federal charges of armed bank robbery after Mendez allegedly made off with nearly a quarter of a million dollars in one of the biggest local bank heists in recent memory.

According to an FBI agent’s affidavit, Jaime, 22, admitted to agents earlier this week that she and Mendez planned the robbery for weeks. Mendez, 27, had been quizzing her about banking procedures for some time and acquired a pistol days before the job, she said. They chose a morning when Jaime, a supervisor at the Lake Street branch, would be opening up for the day.

Then, two days before Thanksgiving last year, as Jaime and a co-worker opened the branch, Mendez forced his way into the building and ordered them to open the vault and a pair of safes, according to a federal criminal complaint. He ordered one employee to drop to her knees and face away from him, while the other helped him load a backpack and duffel bag with cash.

He fled on foot, taking roughly $240,000 in cash — a sum significantly larger than most bank robberies, according to a source familiar with the case.

FBI agents began investigating the couple within days.

The first red flag appeared on Nov. 30 — a call from TCF Bank Corporate Security. Jaime “was not acting ‘appropriately’ as one might after being robbed at gunpoint,” they told the FBI. She also failed to follow normal procedures when opening the bank the morning of the robbery.

One day later, bank security began to notice unusual activity on Jaime’s personal TCF Bank account, including transactions at a separate branch location.

Mendez, meanwhile, had been staying at a halfway house for federal prisoners on probation or supervised release. In addition to convictions for attempted murder and assault, Mendez was completing a federal sentence for a July 2010 armed robbery in Worthington.

On Dec. 9, the same day Jaime quit her job, agents installed tracking devices on both suspects’ cars. They traced the cars to shopping malls, furniture stores and casinos. Before long they uncovered $2,420 of new furniture purchases, a new flat-screen TV, and a $3,375 cash buy-in for Mendez at Mystic Lake Casino over Christmas Eve and Christmas.

And then there was Mendez’s cross-country jaunt to Super Bowl 50. There, on a trip that violated his supervised release for his prior robbery conviction, Mendez allegedly had $15,000 seats — well outside the price range his $17-an-hour construction job could likely afford, according to court documents.

On Tuesday, agents searched Mendez’s Roseville apartment. They found high-end designer clothing and corresponding receipts, new electronics, Super Bowl souvenirs, and a cooler with roughly $117,000 in stacks of U.S. bills, many still bound by bank bands.

A TCF Bank spokesman declined to comment Thursday, saying the bank does not comment on any specifics related to robberies.

The couple’s next date is a Feb. 29 detention hearing at U.S. District Court in St. Paul.

Twitter: @smontemayor