THE private equity firm Cerberus Capital Management has expressed interest in a bid for troubled Canadian smartphone maker BlackBerry, a source familiar with the matter said Wednesday. The source indicated that the investment group was preparing to sign a confidentiality agreement to examine BlackBerry's finances for a possible counter-offer to a $US4.7 billion buyout plan agreed last month. BlackBerry said on September 23 it agreed to the buyout, which translates to $US9 a share, led by Fairfax Financial Holdings Limited but would also consider other offers. Fairfax, a Canadian firm headed by billionaire Prem Watsa, is already BlackBerry's largest shareholder with approximately 10 percent of its shares. Mr Watsa resigned from BlackBerry's board in August when it announced a search for a suitor. Some analysts have said they do not believe the Fairfax buyout will take place, and that it was done to elicit other offers. BlackBerry shares have been trading below the Fairfax offer of $US9, and on Wednesday edged up slightly to close at $US7.96.