By Alex DeMetrick

BALTIMORE (WJZ) — Whoever poisoned 13 bald eagles in Maryland last February remains unknown six months later, and the case is about to be closed.

The bodies were found on a farm field near Federalsburg, on Maryland’s Eastern shore.

READ MORE: State Won't Prosecute Baltimore Officers Who Shot, Killed Armed Man Near Inner Harbor Last Year

“They were fairly recently dead,” said Natural Resources Police spokeswoman Candy Thompson at the time. “There was no sign of trauma. There was no sign of gunshot.”

At a U.S. Fish and Wildlife lab, the cause of death — poison — was found but not released until late last week.

“It’s really hard to fathom how that could happen to such a spectacular bird, and disappointing,” said Mike Parr, of the American Bird Conservancy.

Disappointing because the case will be closed “due to lack of evidence linking anyone to the crime.”

READ MORE: Will Congress Act On Guns After Sandy Hook, Buffalo, Uvalde?

Another case involving five eagles in Delaware will remain open, though.

“There could be more crimes like this,” Parr said. “If there’s a pattern here, if something’s going on, the public can definitely help.”

While $30,000 of reward money was raised while millions viewed a webcam of nesting eagles in D.C. this spring, it did not produce any leads.

Even though the case is closing, “we put a reward out for information leading to a conviction in any of these cases, so it stands,” Parr said.

MORE NEWS: Ferguson And Jones Downplay Possibility Of Special Session For Gas Tax, Blame Oil Companies

Follow @CBSBaltimore on Twitter and like WJZ-TV | CBS Baltimore on Facebook