Numbers 35:30

30 “ ‘Anyone who kills a person is to be put to death as a murderer only on the testimony of witnesses. But no one is to be put to death on the testimony of only one witness.

Read Numbers 35:30 Using Other Translations

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.
"If anyone kills a person, the murderer shall be put to death on the evidence of witnesses. But no person shall be put to death on the testimony of one witness.
“All murderers must be put to death, but only if evidence is presented by more than one witness. No one may be put to death on the testimony of only one witness.