Former Director of National Intelligence James Clapper declined to rule out whether intelligence agencies sent additional informants to spy on members of Donald Trump’s presidential campaign.

“Well, there could have been,” he said when asked by CNN host Jake Tapper on Wednesday about the possibility of other informants. “Never say never, but I’m not aware.”

Clapper has stated that he does not like to use the term “spy” to refer to civilian informants for intelligence agencies.

The idea of additional spies was first raised by former Trump campaign advisor Michael Caputo in an interview on Fox News, reacting to the revelation of the identity of FBI informant Stefan Halper, who spied on Trump campaign advisors.

“He’s not the only person that came at the campaign and the FBI is not the only Obama agency that came at the campaign,” Caputo said.

Clapper denied knowledge of additional spies deployed against the campaign but claimed he did not know about Halper either.

“I mean, the inference was there was another informant from some other part of federal government,” he said. “I’m not aware of that.”