According to police, the suspect named Kevin James Loibl was armed with two handguns, ammunition and a hunting knife when he shot dead Grimmie, 22, at city's Plaza Live Theater late Friday. Loibl opened fire when Grimmie was meeting and greeting fans.
Grimmie had performed with the group Before You Exit before she was admitted to the Orlando Regional Medical Center, but died of her wounds.
"The suspect traveled to Orlando, apparently, to commit this crime, and then had plans to travel back to where he came from," Police Chief John Mina told reporters.
Grimmie's brother Marcus prevented the tragedy from getting worse as he tackled the suspect. Loibl, a 27-year-old from St Petersburg, Florida, shot and killed himself after fatally shooting Grimmie.
"Her brother Marcus is a hero and possibly saved countless other lives," the Orlando Police Department said in a statement.
The statement added that around 120 people were present in the venue at the time. Grimmie's brother escaped unhurt in the accident. Detectives are investigating the cell phone and computer of Loibl in search for a motive.
Police said that bag checks were conducted by unarmed security guards at the concert but they did not discover the shooter's weapons.
"There are no metal detectors. People are not patted down. They open their bags and authorities look inside those bags for weapons," police said.
Most people at the event were "young kids," which "isn't a crowd that you would suspect would be carrying guns," police added.
Police were trying to find out if the shooter knew Grimmie or was a deranged fan. Grimmie had competed in the sixth season of The Voice in 2014. She had released her debut EP Find Me in 2011.
"There are no words. We lost a beautiful soul w/ an amazing voice," the NBC talent show wrote on Twitter.