A possible clue to where the lynx – dubbed the Cairngorms Four – originated from was reportedly found near where they were spotted.
BBC Scotland News understands bedding was discovered with porcupine quills in the straw.
Did whoever release the cats own other exotic animals?
A licence is required under the Dangerous Animals Act to keep lynx.
Local authority Highland Council said last year that no premises in the area had applied for, or were operating under a Dangerous Wild Animal (DWA) licence, suggesting they had come from somewhere else.
Scotland’s nature agency NatureScot also said at the time it had not granted any licences for the reintroduction of lynx.
Police have told BBC Scotland this week that there were no updates in the case and their inquiries were on going.
Asked if RZSS had any theories, Ms Petrie said: “We can’t speculate on how or why the lynx were abandoned as it’s the subject of an ongoing Police Scotland investigation.
“Releasing animals into the wild without the necessary research, planning and consultation is reckless and risks harming both wildlife and local communities.”
She added: “Conservation must be guided by science, collaboration and long-term planning – not by impulsive actions, no matter how well-intentioned they may be.”