Mr. Smith was murdered in Kansas City. The police determined that the time of death was between 11:10 pm and 11:30 pm. Four suspects were questioned: Butler, the butler; Cook, the cook; Ruby, the maid; and Irma, Mr. Smith’s secretary.

The suspects made the following statements:
Butler: I did not do it. Irma did it. Mr. Smith was blackmailing Irma. Ruby and I were watching television together from 10:10 p.m. until 12:30 a.m.
Cook: I am innocent. Irma was being blackmailed. Butler murdered Mr. Smith. I saw Irma leave the house at 10:00 p.m.
Ruby: I am innocent. Butler and I were watching television together at the time of the murder. Irma was being blackmailed. I saw Irma speaking to Mr. Smith at 9:30 p.m. on the night of the murder.
Irma: I did not kill Mr. Smith. I was not being blackmailed. I was in St. Louis during the entire night of the murder. Ruby is the murderess.

If each suspect made exactly two true statements and told exactly two lies, determine who killed Mr. Smith.