How could you prevent someone else from taking credit for an article that is sent to the newspapers?

Two Words: copyright and plagiarism.

If you can prove you are the author, you can register your copyright and sue for statutory damages or actual damages and bring criminal charges of copyright infringement where the copied work was published for profit.

You can also contact the ombudsman with the proof and have the other reporter charged with plagiarism, which could mean loss of job, future contracts, or other administrative sanctions.