Senators on Capitol Hill recently introduced the Back the Blue Act of 2017 with the laudable objective of supporting public safety officers.

While that intention is noble, the bill unfortunately omits something crucial: the ancient element of crime known as “mens rea” (Latin for “guilty mind”).

Mens rea distinguishes between tragic accidents, or innocent mistakes, and malicious crimes. It ensures that people are criminally punished only for conscious violations of law or intentional, morally culpable conduct.

The Back the Blue Act of 2017 would make it a federal crime to “kill, or attempt or conspire to kill” any federally funded public safety officer “while that officer is engaged in official duties, or on account of the performance of official duties.”

The bill carries criminal fines and 10 years to life in prison for injuring these officers, and 30 years to life—or the death penalty—if an officer dies.

Thus, the bill criminalizes three separate types of conduct:

1) Killing an officer.

2) Attempting to kill an officer.

3) Conspiring to kill an officer.

The attempt and conspiracy offenses proscribed in the bill are specific intent crimes, meaning that before the government can obtain a conviction, it must prove that a defendant intended to commit the proscribed conduct.

The problem is that the term “to kill” has no intent component. The Merriam-Webster dictionary defines “kill” as “to cause the death of.”

That stands in sharp contrast to “murder,” which is defined as “the crime of unlawfully killing a person especially with malice aforethought.”

Because the bill does not require that a defendant intend to kill or even know his “victim” was a “federally funded public safety officer,” its severe penalties would apply if someone accidentally crashed into an officer with a bicycle, motorcycle, or car, or unknowingly served him contaminated food, and the officer died.

In short, any tragic accident that resulted in the death of a federally funded public safety officer could trigger severe federal criminal liability up to and including the death penalty.

According to The Economist, accidents are a leading cause of death in the United States, and many officers die each year in traffic-related fatalities (although there is no breakdown as to how many of these were accidental).

We all want to support our brave men and women in blue and other public safety officers, but this bill stretches federal criminal liability just a bit too far.

For comparison, the Blue Lives Matter Act of 2016 failed to pass through the House last year, but would have made it a federal crime “to knowingly cause bodily injury to any person, or attempt to do so, because of the actual or perceived status of the person as a police officer” (emphasis added).

Setting aside the issue of whether such a bill is necessary (intentionally killing a police officer is already a crime that is vigorously enforced in every state), at least the 2016 version did not criminalize accidental conduct.

Perhaps the difference between the two versions was simply an oversight, in which case it should be corrected. While it is likely that federal authorities would not prosecute an individual who accidentally killed a police officer, such things should not be left to chance.

Supreme Court Justice Clarence Thomas wrote in Staples v. United States (1994), “the requirement of some mens rea for a crime is firmly embedded” in historic common law rules, and “[t]he existence of a mens rea is the rule of, rather than the exception to, the principles of Anglo–American criminal jurisprudence.”

That general rule was perhaps best expressed by Justice Oliver Wendell Holmes, who famously observed that “even a dog knows the difference between ‘being stumbled over and being kicked.’”

This Congress should heed the long-held wisdom, expressed by Harvard Law School professor Francis B. Sayre, “that subjecting defendants ‘entirely free from moral blameworthiness to the possibility of prison sentences is revolting to the community sense of justice,’” and “no law which violates this fundamental instinct can long endure.”