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A picture began to emerge on Tuesday of the 21-year-old charged with 10 counts of murder in connection with Monday's mass shooting at a Colorado grocery store, but his motive remained unclear.

BOULDER COUNTY DA MICHAEL DOUGHERTY: "Why did this happen? We don't have the answer to that yet."

Boulder County District Attorney Michael Dougherty said at a news conference that the suspect, identified by police as Ahmad Al Aliwi Alissa of Arvada, Colorado, was expected to be released from the hospital later on Tuesday and transported to jail, after suffering a leg wound in an exchange of gunfire with responding police officers at the King Soopers outlet in Boulder.

A more detailed picture also emerged of Officer Eric Talley, an 11-year veteran of the Boulder police force who had recently been looking for a less dangerous job, according to a statement released by his father.

Talley was the first on the scene and died in the attack.

BOULDER POLICE CHIEF MARIS HEROLD: "This officer had seven children, ages 5-18. I just had that officer's whole family in my office two weeks ago to give him an award. And so it is personal. This is my community. I live here."

The other nine victims range in age from 20 to 65. The bloodshed marked the country's second mass shooting in less than a week, after a killing spree at spas in the Atlanta area that left eight people dead, bringing new attention to gun violence.

U.S. PRESIDENT JOE BIDEN: "We have to act."

Later on Tuesday, President Joe Biden called for tighter gun control measures and a ban on assault weapons.

BIDEN: "I don't need to wait another minute, let alone an hour, to take common sense steps that will save the lives in the future and to urge my colleagues in the House and Senate to act."

Flags at the White House were at half staff until sunset on Monday to commemorate the Atlanta shooting victims. They flew at full staff for a few hours on Tuesday morning before being lowered again to mark the Boulder killings.