If anyone kills a person, the murderer is to be put to death on the testimony of the witnesses. But no one is to be put to death based on the testimony of a lone witness.
KJV
Whoso killeth any person, the murderer shall be put to death by the mouth of witnesses: but one witness shall not testify against any person [to cause him] to die.
ASV
Whoso killeth any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die.