Stephen Feinberg, co-founder of Cerberus Capital Management LP, is exploring a bid for Freedom Group, the Bushmaster rifle manufacturer being auctioned off by his New York-based buyout firm, three people familiar with the matter said on Tuesday.

Facing mounting pressure from the public as well as investors in its funds, Cerberus said in December it would look to sell Freedom Group, which made the AR-15 type Bushmaster rifle that was used in the Newtown, Connecticut shootings.

Feinberg and other senior partners at Cerberus are working to put together a consortium to make a "stalking horse" bid, or the opening bid, for Freedom Group, and has approached other wealthy individuals to join his group, the people said.

Cerberus declined to comment on behalf of Feinberg.

Investment bank Lazard Ltd, which is running the auction, declined to comment, while representatives of Freedom Group could not be reached for comment.

(Reporting By Olivia Oran, Greg Roumeliotis and Martine Geller in New York; Editing by Soyoung Kim, Paritosh Bansal and Ryan Woo)