Who is Marcus Grimmie? Christina Grimmie's Brother Hailed a 'Hero' for Tackling Shooter

— -- The brother of singer Christina Grimmie, who was shot and killed after a concert in Florida Friday night, is being hailed as a hero by law enforcement and fans alike.

Marcus Grimmie was with his sister, who was a contestant on "The Voice" in 2014, when a gunman walked up and shot her at Orlando's Plaza Live Theater. Christina Grimmie and the band Before You Exit were signing autographs and selling merchandise after their show ended at 10 p.m.

Police said Marcus Grimmie immediately "tackled" the man -- later identified as Kevin James Loibl, 27, of St. Petersburg, Florida -- after he opened fire, possibly saving the lives of countless others.

At a news conference today, Orlando Police Department Chief John Mina said Marcus Grimmie's actions were "heroic."

The gunman fatally shot himself during the struggle with Marcus Grimmie and was pronounced dead at the scene, police said.

"Her brother is a hero," Orlando Police Department public information officer Wanda Miglio said during an earlier press briefing this morning.

Police said Loibl had two handguns, loaded magazines and a hunting knife. He traveled to the concert venue from another part of Florida specifically to shoot Christina Grimmie, although there was no indication her knew the singer personally, officials said.

Grimmie was transported to a local hospital, where she later died from critical injuries, police said.

Investigators are searching Loibl’s computer and other belongings to determine a motive for the deadly shooting. It’s unclear how he got into the concert venue, where unarmed security guards check bags and purses, officials said.

Some of Christina Grimmie's fans who had been at the concert venue also expressed gratitude to her brother Marcus on social media. One fan on Twitter mourned the singer's death, but said "it easily could have turned into a shooting rampage" if it weren’t for Marcus Grimmie.

"Thank you Mark Grimmie for saving my life as well as some other incredibly brave friends and fans. We appreciate you," the user wrote. "Mark, you are a hero."

Marcus Grimmie has posted photos on his Instagram page celebrating his sister's music career in recent years. He plays guitar and often accompanied his sister in several of her videos posted on YouTube, where the singer made a name for herself long before she impressed all four judges on "The Voice."

ABC News' Benjamin Stein contributed to this report.