In the US they can.
Yes. A participant in a crime where someone was murdered can be executed even if he was not the killer.
Although no one is on death row for the following crimes, capital offenses exist in state law for various other crimes:
Treason (Arkansas, Calif., Colorado, Georgia, Illinois, Louisiana, Mississippi, Missouri, Washington)
Aggravated kidnapping (Co., Idaho, Il., Missouri, Mont.)
Drug trafficking (Fl., Missouri)
Aircraft hijacking (Ga., Mo.)
Placing a bomb near a bus terminal (Mo.)
Espionage (New Mexico)
Aggravated assault by incarcerated, persistent felons, or murderers (Mont.)
Here's a list of people who did not directly kill the victim, but were executed anyway:
1. Doyle Skillern TX 1/16/1985
2. Beauford White FL 8/18/1987
3. G.W. Green TX 11/12/1991
4. William Andrews UT 7/30/1992
5. Carlos Santana TX 4/23/1993
6. Jessie Gutierrez TX 9/17/1994
7. Gregory Resnover IN 12/8/1994
8. Steven Hatch OK 8/9/1996
9. Dennis Skillicorn MO 5/20/09
10. Robert Thompson TX 11/19/09