Hi,
As I understand it, the whole idea of Aikido being non-lethal, and not injuring your attacker, is very much an idealised philosophy that O-Sensei developed later in his expression of Aikido. Prior to World War 2, the school of Morihei Ueshiba was known as the Jigoku Dojo, or Hell Dojo, and it was a place only for the truly tough. Ueshiba Sensei was an experienced Martial Artist of a number of classical systems, which definately included lethal techniques, and I have little doubt that Ueshiba Sensei incorporated at least some of it into the earlier expressions of his Art.
To find a similar form of Aikido to that of the Jigoku Dojo, I would look to the Yoshinkan organisation, founded by Gozo Shioda, who left the dojo of Ueshiba not long after WWII, as he believed that O-Sensei was unnecessarily "softening" the art, and wanted to preserve the original "Martial" aspect. After WWII, Ueshiba Sensei began re-evaluating his personal art, and his veiws on the concepts of inflicting pain and violence on other human beings, basically deciding that in an ideal world, causing unnecessarily pain was to be avoided.
The important thing here is the word "unnecessary". If an attacker is assaulting you, and means to do you major harm, or even kill you, it is unrealistic to believe that you should respond without causing any injury, and Ueshiba Sensei would certainly have known that. However, to create an art which sought to deliberately cause pain, maiming, or even death, was unethichal in the views of Ueshiba Sensei. But sometimes the most ethical and compassionate action you can take is to thoroughly and completely convince an attacker from continuing down their destructive path (and that can mean a truly violent action).
So, I feel that if you look for them, you will find lethal techniques in Aikido, however, I don't think you will find them commonly taught, and if they are, it will only be at a high level. But I would ask why you would need them? Are you really having that big an arguement wtih your next door neighbours? I hope not.
By the way, any Aikido practitioners, please feel free to correct anything I've gotten wrong here, I'm hoping it's not too much.