Ms. Tribble, who holds a doctorate in meteorology, was assigned to Puerto Rico for a year, where she was the agency’s energy sector lead. She was also a Homeland Security adviser during the Obama administration.

According to prosecutors, Mr. Ellison lavished Ms. Tribble with gifts in exchange for her influence inside FEMA that was used to give Cobra an advantage. The “stream of benefits” ranged from a helicopter ride over Puerto Rico to the securing of an apartment in New York, the authorities said.

They also included personal security services; the use of one of Mr. Ellison’s credit cards; airplane tickets, including one first-class ticket from San Juan, the Puerto Rican capital, to New York; and hotel stays in Fort Lauderdale, Fla., and Charlotte, N.C. Mr. Ellison and Ms. Tribble traveled together and stayed in the same room, Ms. Rodríguez Vélez said. One of their itineraries mentioned in the indictment referred to travel involving “you,” “me” and “us.”

The two defendants tried to conceal the gifts by using Mr. Ellison’s credit card. Ms. Tribble communicated with Mr. Ellison using her personal email and cellphones, including a disposable cellphone, according to the indictment.

In return for the gifts, Ms. Tribble is accused of performing official acts to advance Cobra’s interests. For example, according to the indictment, in February 2018, after the Puerto Rico Electric Power Authority reported an explosion at a substation in Monacillo, P.R., that left several municipalities without power, Ms. Tribble insisted that the public utility hire Cobra to make repairs or risk not getting reimbursed by FEMA — even though leaders of the utility insisted they could do the same work at a far lower cost.