What should other journalists do, when faced with allegations of plagiarism?

"Journalists are accountable to their readers, listeners, viewers and each other.

Journalists should:

Clarify and explain news coverage and invite dialogue with the public over journalistic conduct.

Encourage the public to voice grievances against the news media.

Expose unethical practices of journalists and the news media."

http://www.spj.org/ethicscode.asp