As Knoxville, Tennessee, continued grappling with the killing of rising high school football star Zaevion Dobson, President Barack Obama took to Twitter to repeat his call for stricter gun control laws.

"Zaevion Dobson died saving three friends from getting shot," Obama wrote Sunday from Hawaii, where he arrived Friday for the holidays. "He was a hero at 15. What's our excuse for not acting?"

Zaevion Dobson died saving three friends from getting shot. He was a hero at 15. What's our excuse for not acting? https://t.co/hn98uGsjKZ — President Obama (@POTUS) December 20, 2015

Zaevion was struck by three bullets after diving atop three girls to shield them from the hail of gunfire. All three were uninjured; Zaevion later died at a hospital.

Police described the shooting as indiscriminate, saying the gunmen "randomly fired multiple times into a crowd."

Obama's message Sunday is one he has repeated often repeated this year.

After the October shooting at a community college in Oregon, he said that "thoughts and prayers are not enough" to "prevent this carnage from being inflicted some place else in America next week or a couple months from now."

After the shootings this month in San Bernardino, California, he described a gun law loophole as "insane" and declared that Americans "will not be terrorized" by mass shootings.

Earlier this month, an adviser said the White House is crafting a background check proposal that wouldn't require congressional approval.

Meanwhile, in Knoxville, a memorial fund for Zaevion had collected nearly $60,000 from 1,455 donors Sunday. A note on the page remembered his final act simply: "Would I/you be this brave?"