The death penalty should be banned because humans do not have the right to take away a life. Only God has the right to make and take a life. For example killing a murderer does not make up for the death of the victim. Just like two wrongs don't make a right, two deaths don't make it right.
This should not simply be a religious debate as religion should not play a factor in government. Although two wrongs do not make a right, some men are too dangerous to be kept alive. For example, Nikita Fouganthine, a 50 year old Finnish serial killer, escaped from jail in 1994 and killed more people before being sentenced to jail. Had he been put to death, this man would not have killed more innocent people. Additionally, prison is meant to be a correctional facility. Those killers who are on death row are not going to be corrected., like Fouganthine as he has clearly not shown repentance.
Although that is one situation where the death penalty may have been useful, at the same time if our country shifts from essentially taking the easy way out by killing the suspect instead they could work more towards securing the prison from future incidents such as your example. Yes prison is supposed to be a correctional facility and in some cases it does help to improve the victim, and if it doesn't I believe that it can serve as a sentence of lifetime missery. This way the suspect ends up with a larger consequence for their actions instead of being killed and freeded of their tortuous life.
First off, the death penalty would only be used in extreme cases, not necessarily a common criminal or a one time killer. The death penalty is not an easy way out. The killers do suffer when they die. Additionally, it is used to put fear into the minds of potential killers and stop future crimes. If the criminals are scared, they may think twice about a senseless killing, and not do so. Lastly, jail is not a torturous life. It is not a prison camp, like in Escape from Camp 14. Prisoners get three meals a day, and get leisure time to work out. In comparison, living as a homeless man on the streets is much more difficult, threatening, and unpleasant. For some, life in jail may be an upgrade.