Review the list of sources the student should have provided at the end of their paper. If the student has used Internet sources and provided URL addresses, visit these sources. Read the student's paper against them, checking to see if they have been too closely copied from or inappropriately cited. You may find that a URL leads to a different source or does not work. Broken or mistyped URLs in a student's list of references can be an indication that a student is trying to hide plagiarized sources.
If the student has not used Internet sources or you cannot find evidence of plagiarism based on the Internet sources she provided, type suspect sentences or phrases from the paper into the Internet search engine of your choice. If the student has plagiarized from a source archived on the Internet, your search should produce a variety of examples. Again, compare these sources to your student's paper, looking for evidence of plagiarism.
Should your Internet searches prove fruitless but you still suspect plagiarism, as a last resort, look up any print sources the student has cited and check them against your student's paper.