A man walked into Lopez Tires in Salt Lake City, Utah, last week, announced his intention to “kill Mexicans” and then beat the shop’s owner and his teenage son with a metal pole so severely that the younger man was sent to the hospital in critical condition, the authorities said. A suspect was quickly caught, but under Utah law he cannot be charged with a hate crime.

The attack on Jose Lopez and his son Luis has drawn new attention to the hate crimes law on the books in Utah, which has long frustrated law enforcement officials because it can be applied only to misdemeanors, not felony crimes like murder or serious assault, rendering it largely ineffective.

“The statute that we have is such an untenable and unworkable statute that we have not had a successful prosecution of a hate crime for the last 20 years at the state level,” said Sim Gill, the district attorney for Salt Lake County. “It is worthless. It is not worth the paper it is written on.”

A man walked into the Lopez family’s business on Nov. 27 and “said he wanted to kill Mexican guys,” said Mr. Lopez, who suffered a laceration to his arm in the attack.