This could be true. But being called a suspect doesn't guarantee that charges will be filed. And a person doesn't need to be designated as a suspect in order for LE to file charges. The term is not a legal prerequisite to anything. LE does not acquire any greater rights by naming someone as a suspect. That's why, in the technical sense, the term means nothing.
I suppose that LE might be signalling that their case against Casey got stronger, and that this is one way to send that signal without necessarily revealing their actual hand. But the term itself has no legal effect whatsoever.
But police say the terms aren't always interchangeable.
Though persons of interest often graduate to suspects and are charged or getting ready to be charged with a crime, police may use the phrase because they're trying to find someone of a certain description who happened to be near the scene of a crime.
It could refer to a suspect's friend, they say. Sometimes a person of interest can be ruled out as a suspect after investigation.
Being labeled a "person of interest" can be harmful.
Just how the phrase became a staple of cop-speak is unknown.
"We have phrases that seem to come into popularity out of nowhere, such as 'perp walk' and 'person of interest,'
Most experts, though, point to the bombing during the Olympics in Atlanta in 1996 as the point when police began using "person of interest" in place of "suspect."
The FBI leaked the name of security guard Richard Jewell as a possible suspect in the bombing. He was later cleared and sued various news outlets over the damage to his reputation.
CNN agreed to pay an undisclosed amount to Jewell and his mother to forestall a lawsuit.
NBC also reached an out-of- court settlement with Jewell, paying him an amount The Wall Street Journal reported as more than $500,000.
Some attorneys and pundits believe investigative agencies became wary of using "suspect," turning to "person of interest" as a milder reference until charges are eminent.