Joshua Barnwell was shopping with a friend at the Allen Premium Outlets Mall in the Dallas suburb of Allen, Texas, when he said he heard "two pops" go off. Shortly after, "massive rapid gunfire" rang out, and he knew there was a shooter. 

He said he quickly took cover behind a concrete pillar with his friend and called 911. He also sent an SOS message to his emergency contacts, informing them of the situation. 

The shooter was heavily armed with an AR-style rifle and wearing body armor, according to law enforcement sources. Police said he fired dozens of rounds at customers before being confronted and killed by an officer who was at the mall for an unrelated call.

Eight people were killed, including one person Barnwell said he tried to help.

"I started doing chest compressions and mouth to mouth," he told "CBS Mornings" Monday. "When I did that, the amount of blood that came out of her backside, because her front side appeared clear, but the amount of blood that came out of her backside was unbelievable. And I knew at that time that she had left us."

Barnwell described seeing multiple bodies on the floor and a young boy "who was just covered from head to toe in blood — in what I would later learn [was] the blood of his mother and father." 

When asked how he was processing the traumatic event, Barnwell said he tends to turn to "just a pure logic."

"In a situation like this I try to take out any emotion personally and just let it process through my mind in a logical format, even though it appears illogical."

Investigators are looking into whether the gunman, identified as Mauricio Garcia, 33, was motivated by domestic violent extremist ideals, according to a law enforcement source. 

Two sources also confirmed to CBS News that the shooter had a patch on his clothing with the letters "RWDS," which stands for "Right Wing Death Squad" —  believed to be a right-wing neo-Nazi group.

Garcia was living in a motel and working as a security guard at the time of the shooting, sources told CBS Texas. He did not have a serious criminal record. Authorities raided a house late Saturday night in Dallas that belonged to the gunman's parents, sources told CBS Texas. Authorities also searched the Extended Stay motel where he had been living, according to CBS Texas. 

S. Dev contributed to this article.