On Friday, about 72 hours after Annie Le GRD ’13 was last seen entering 10 Amistad St. through its front doors, two Yale Daily News reporters walked through that same entrance.

They showed their Yale identification cards to a security guard and took the elevator down to the building’s basement. They walked out of the elevator and scoured the basement for information about what was, at the time, thought to be a missing person’s case. At one point, a group of investigators wearing FBI jackets passed them in the hallway but said nothing to them.

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All the while, Le’s remains were hidden behind a wall somewhere on that same floor. But the building remained open to Yale faculty, staff and students until Sunday — five full days after Le was last seen — when investigators found Le’s corpse.

“That’s a no-no,” said Henry Lee, a retired commissioner of the Connecticut Department of Public Safety and a director of the Henry Lee Institute of Forensic Science at the University of New Haven. “That’s not supposed to happen.”

In a series of interviews conducted yesterday, law enforcement experts from around the country said they were surprised and concerned that authorities did not seal the research facility on Amistad Street as soon as it became clear that Le was missing and that a crime could have been committed inside the building.

But the circumstances surrounding Le’s disappearance were unclear, and investigators initially proceeded on the presumption that Le was missing or kidnapped — not trapped inside the laboratory at 10 Amistad St.

“For the first couple of days it was a missing person” case, New Haven Police Chief James Lewis told the New Haven Independent on Monday. “We have missing persons all over the country all the time. You can’t shut down a building for that.”

Indeed, as of Jan. 1, there were 102,764 missing persons in the United States, according to the FBI. But the experts still suggested that the building should have been sealed earlier than it was.

“Generally it’s a good idea to prevent people from coming into and out of a building where a crime occurred,” said Larry Williams Sr., a forensic security consultant and retired New Orleans police detective. “I would be very reluctant to let anyone go in that building or go out of that building.”

After all, Williams said, people might remove evidence — intentionally or unintentionally — or they could contaminate the evidence left at the scene.

“Police could look back on this later and say, ‘What if we’d had it tighter earlier?’ And at that point, you may never know,” said retired FBI agent Brad Garrett, who was one of the principal investigators in the Chandra Levy case. Garrett characterized the decision to close off access to the building as a “judgment call.”

For his part, University President Richard Levin said in an interview Monday night that access to the basement was limited before the rest of the building was sealed.

“Even in the first couple days when people were allowed in the basement there were law enforcement officials all over the place,” Levin said. “It was not unprotected.”

New Haven Police Department spokesman Joseph Avery pinned the decision to keep the building open on the Yale Police Department.

“It was all up to the Yale PD, not us,” he said.

James Perrotti, chief of the Yale Police Department, did not respond to repeated requests for comment last night.In an e-mail to the campus community, Vice President and Secretary Linda Lorimer said Monday that, in fact, the building still remains open to “those with essential research responsibilities,” though she said police are escorting those people in and out of the building. The building is otherwise closed to the public and press.

Yale officials have been hesitant in recent days to reflect on the investigation, saying it’s still ongoing and that it remains too early to know what — if anything — had gone wrong.

But Perrotti did acknowledge in an interview Thursday that the University could have moved more quickly to alert people on campus of Le’s disappearance.

Le, who was last seen entering the Amistad Street facility at 10 a.m. Tuesday, was reported missing at about 9 p.m. that night, though police did not inform media outlets until Wednesday afternoon and did not send a message to the entire campus community until Thursday morning.

“We would try to get that out earlier in the future,” Perrotti said of that e-mail. “Hindsight is always 20-20.”

Reporting was contributed by Harrison Korn, Zeke Miller and Victor Zapana.