(NewsNation) — Police in Lewiston, Maine, are searching for person of interest Robert Card after a shooting that left 18 people dead and 13 injured. But what’s the difference between a person of interest and a suspect?

Police use person of interest to describe anyone potentially connected to a crime, without having sufficient evidence to label that person a suspect.

“So when we say a person of interest, it’s just somebody who may have information about the crime,” NewsNation legal contributor Jesse Weber explained. “A suspect is when the evidence leads to that as the perpetrator of the crime.”

Weber said it’s hard to say exactly why police aren’t naming Card a suspect at this point.

Joshua Skule, a senior executive with the FBI, told NewsNation police may be using the term as they attempt to gather more evidence on the shooting.

“I believe they’re calling him a person of interest because they don’t have anything substantive beyond a grainy photo to say it’s Card,” Skule said.

He added that law enforcement officers would be working on obtaining warrants that would allow them to gather more evidence to officially identify a suspect.

The term person of interest doesn’t have the greatest history. In the 1960s, law enforcement officials used the term when assembling secret dossiers on Vietnam War protesters and civil rights activists and other persons of interest.

The term began to be used more widely in 1996, after police named security guard Richard Jewel a suspect in the Olympic Park bombing in Atlanta. Jewell faced intense media scrutiny over his assumed guilt but was never charged and was eventually exonerated. Jewell successfully sued a number of those who accused him, including media outlets.

However, the term began to be criticized during the 2001 anthrax attack investigation, after U.S. Attorney General John Ashcroft used it to refer to Dr. Steven J. Hatfill, since confusion over the two terms could lead people to believe there was more evidence of someone’s guilt than might actually exist. Hatfill was officially exonerated in 2008.

Whatever the label, Skule told NewsNation that publicly naming someone is part of an effort by law enforcement to find and question someone quickly.

“Whether they call them a suspect or a person of interest, they’re trying to bring this person into custody safely as quickly as possible,” he said.