Dallas gunman wrote on wall with blood during police negotiations

DALLAS -- A makeshift memorial continues to grow in Dallas where five police officers were killed by a sniper last Thursday.

CBS News has learned that the gunman taunted police during two hours of negotiations, before authorities killed him with a robot bomb.

The killer said he was targeting police in revenge for the fatal police shootings of two black men in Minnesota and Louisiana last week.

Those deaths led to tense protests -- and dozens of arrests -- in Saint Paul, and Baton Rouge, on Saturday night.

After the initial rounds of gunfire, Dallas police chief David Brown said in an interview Sunday, the gunman laughed at police negotiators and scribbled letters on a wall with his own blood.

Micah Xavier Johnson, an Army veteran, put his military training to use when he targeted police officers, killing five, and turning parts of downtown Dallas into a war-zone.

Twenty-five-year Dallas police veteran James Dupuch rushed to the scene.

"It was painful to see officers being picked up and placed in squad cars," he said. "We don't ever see that, hardly ever."

On the streets, it was chaos.

The city remains on edge, a threat to police headquarters Saturday night had officers on high alert, though it turned out to be a hoax.

Across Dallas Sunday, church services were dedicated to the fallen officers.

"Life is so fragile. One blink and the person you love is gone," Bishop Thomas Dexter "T. D." Jakes said.

Members of a church within the sealed-off crime scene gathered on a nearby corner to pray.

Three days after the attack, about 20 square blocks of downtown Dallas are still shut down -- and parts could remain closed well into the work week.