A 21-year-old man has been accused of using a semiautomatic rifle to open fire in a local supermarket on Monday (22Mar21), killing 10 people, including a Boulder police officer.
The tragedy emerged less than a week after eight people were killed by a lone gunman in the Atlanta, Georgia massage parlour massacre, and the latest shooting spree has fired up gun control activists.
"My heart is with the families affected by the tragedy in Boulder," mother-of-two Biel posted on Twitter. "While we still don't have all of the information, one thing is very clear... we need #gunreformnow. Enough is enough."
"Star Wars" icon Hamill also used social media to call for "#UniversalBackgroundChecks" as he demanded, "#BanAssaultWeaponsNow," after sharing a drawing of a Colorado map and adding a string of broken heart emojis.
As U.S. President Joe Biden urged members of Congress to pass gun reform legislation now, former First Ladies Michelle Obama and Hillary Clinton expressed heartache at the senseless killings and voiced support for laws to curb gun violence.
Similar calls were made by Nancy Sinatra and newswoman Maria Shriver while tributes to the lives lost in the attack came from the likes of comedienne Wanda Sykes, rapper Juicy J, pop duo Aly & AJ, and country superstar Luke Bryan, who tweeted, "Tragedy struck in Boulder, CO tonight. My heart goes out to the victims and their families. Praying for healing. #BoulderStrong."