When a sentence begins with a subordinate clause, a comma is usually needed to separate it from the main clause:

Confusion can arise when the comma is left out:

In some cases, such as short introductory elements that can’t connect to the next word or words in a misleading way, the use of a comma is a judgment call. In general, however, using a comma will help readers find the beginning of the main part of the sentence.

In England in the 1980s, DNA evidence proved that a man who had confessed to killing a teenager was innocent and that another man was guilty.

Similarly, principles behind forensic linguistics led a U.S. appeals court to overturn the 1963 conviction of Ernesto Miranda.