The body cameras were shut off before agents put Reyes Aguilar in the back of an SUV and took him to a cemetery — which they had used as a “staging ground” for their operations.What happens next is a mystery that took center stage in an unusual hearing in federal court Monday, as a magistrate judge probed agents for answers: What happened at the cemetery? Why was he taken to a cemetery in the first place? And what, exactly, became of Reyes Aguilar’s wallet?US Magistrate Judge Jennifer Boal held the hearing seeking an answer to that very question — what happened to Reyes Aguilar’s wallet? — but the hours’ long proceeding also served as a portal into the inner workings of an immigration arrest that had been sharply criticized by Lynn officials at the time, for the way it was carried out outside an elementary school during morning dropoff time.In a flurry of orders leading up to the hearing, Boal said the government violated her order to return Reyes Aguilar’s property months ago, and the apparent lack of ICE procedures for preserving property it seizes during arrests “frankly strain credulity.”Boal put such an emphasis on the case that US Attorney Leah B. Foley appeared in court on behalf of the government, a rarity for the state’s top federal attorney to assume the role of a line prosecutor in such a case.A parade of federal agents testified that Reyes Aguilar was a passenger in a utility van that was stopped during a high-profile immigration enforcement sweep in the area, because it was registered to an immigrant who had reentered the country after being deported. The driver fled, and Reyes Aguilar and another passenger were arrested.They described Reyes Aguilar as aggressive, belligerent, and combative. They also said it was standard practice to take people arrested during the immigration sweep to the Pine Grove Cemetery in Lynn, which was used as a staging area to avoid the public and also as a place where agents would often hand detainees over to a private contractor for transport to an immigration detention facility.Reyes Aguilar, 40, a Honduran native and lawful US resident, was arrested for allegedly assaulting a federal agent. Federal prosecutors dropped the charge the following day. He later pleaded for the return of the key to his truck and wallet. As of Monday’s hearing, no one can say what happened to them.Government lawyers argued that the hearing wasn’t necessary because agents had concluded the wallet and key were irretrievably lost after an exhaustive search, and that the FBI had already compensated Reyes Aguilar $725, which covered the cost of the wallet, the key, and an unspecified amount of money.Boal ordered the hearing anyway, saying she wanted to hear from all the agents from the Department of Homeland Security, the FBI, and DEA who were involved in the arrest to determine what happened and provide an incentive for the government “to appropriately preserve and account for seized property.”She said she was still weighing whether to impose sanctions against the government, and will set a date to hear arguments from the government and defense lawyers.Reyes Aguilar, who owns a carpentry business, did not attend Monday’s hearing, and a lawyer who represents him said he declined to comment. In an interview with Telemundo after his arrest, he claimed he was beaten by agents at the cemetery and showed bruises and scratches on his body. His wife, who delivered the couple’s third child a week after his arrest, told the station her husband has no criminal record.During Monday’s hearing, agents testified Reyes Aguilar was injured while on the ground and resisting arrest after being pulled from the van.Body camera footage shows Reyes Aguilar bleeding from the face after being forced to the ground, and agents struggling to handcuff him and then looking for alcohol wipes and hand sanitizer. DEA special agent Stephen Walsh testified that when he approached the van’s passenger door and asked Reyes Aguilar for his identification, he “shoved the car door into myself” and the pair struggled as he pushed him back inside the van.He said Reyes Aguilar kept reaching into the middle of the van and he thought he was reaching for a weapon. He pushed him back into the van.Walsh said Reyes Aguilar was “very aggressive” and it took about five agents to bring him to the ground and put handcuffs on him.Julie-Ann Olson, a lawyer at the Federal Public Defender’s office who represents Reyes Aguilar, played video footage from body cameras in court that showed her client open the door, prompting Walsh to quickly step back and order him to stay in the van.“To me it looks like he’s just opening the door,” said Olson, questioning whether Reyes Aguilar was given an opportunity to present his identification before he was taken into custody.Olson also showed Walsh a photo taken from the body camera video of him standing beside the van, and asked, “Can you describe what’s in your hand?”“It appears to be a wallet,” Walsh said.“Do you know whose wallet it is?” Olson asked.“I don’t,” Walsh said, acknowledging that he was looking at a wallet, but didn’t remember what he did with it.FBI agent Brian Gutierrez testified that when he arrived at the cemetery, where Reyes Aguilar had been brought, he saw him sitting in the back seat of a car with his seat belt on and noticed “a bulge in his right pocket.”The agent said he retrieved a wallet from Reyes Aguilar’s pocket and handed it to an agent who was standing behind him while he conducted a search for more items. He said he didn’t recall who took the wallet from him.ICE officer Kelsey Leydon testified that someone — she could not recall who — removed Reyes Aguilar’s green card and Massachusetts driver’s license from his wallet and handed them to her at the cemetery. She turned those over to the FBI, which later returned them to Reyes Aguilar’s lawyer.She said she doesn’t recall ever seeing his wallet or key.Shelley Murphy can be reached at shelley.murphy@globe.com. Follow her @shelleymurph.