Ebel's father didn't return an after-hours phone message left at his business.
Clements came to Colorado in 2011 after working three decades in the Missouri prison system. Missouri Department of Corrections spokeswoman Mandi Steele said Thursday the department was ready to help in the probe if asked.
"Tom regularly commented that corrections is inherently a dangerous business, and that's all that I'll say," Morgan, who worked closely with Clements, said earlier.
Officials in positions like Clements' get a deluge of threats, according to people who monitor their safety. But it can be hard sorting out which ones could lead to violence. A U.S. Department of Justice study found that federal prosecutors and judges received 5,250 threats between 2003 and 2008, but there were only three attacks during that time period.
The last public official killed in Colorado in the past 10 years was Sean May, a prosecutor in suburban Denver. An assailant killed May as he arrived home from work. Investigators examined May's court cases, but the case remains unsolved.