were there any other murders he was involved in?
Yes. He also shot Michael Burdell
Ronnie Lee Gardner
In October 1984, Gardner killed Melvyn John Otterstrom during a robbery in Salt Lake City. While being moved in April 1985 to a court hearing for the homicide, he fatally shot attorney Michael Burdell in an unsuccessful escape attempt. Convicted of two counts of murder, Gardner was sentenced to life imprisonment for the first count and received the death penalty for the second. 
who was executed by firing squad in utah Ronnie Lee Gardner who is the aforesaid person? He was an American criminal why was he executed? For killing a man during an attempted escape from a courthouse in 1985
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Ronnie Lee Gardner [SEP] Introduction
Convicted of two counts of murder, Gardner was sentenced to life imprisonment for the first count and received the death penalty for the second. The state adopted more stringent security measures as a result of the incident at the courthouse. While held at Utah State Prison, Gardner was charged with another capital crime for stabbing an inmate in 1994. However, that charge was thrown out by the Utah Supreme Court because the victim survived. In a series of appeals, defense attorneys presented mitigating evidence of the troubled upbringing of Gardner, who had spent nearly his entire adult life in incarceration.