Keith Fahrney was driving home from his trigonometry class at Rock Valley College Wednesday afternoon when he saw a commotion outside his neighbor's home.
"She kind of turned towards me, and her face was just bright red with blood," Fahrney told ABC News.
Fahrney didn't know it at the time, but he had happened upon a brutal stabbing spree in his neighborhood in southeast Rockford, Illinois, that police said left four people dead and several others, including his neighbor, injured.
MORE: 4 dead, 1 in critical condition after Illinois stabbing spree; suspect in custody, officials sayFahrney said he stopped and got out of his Jeep to see how he could help, when a man standing over the woman bolted and got into the Jeep.
"I opened up the door, grabbed him by the shirt and threw him down on the ground right and then he kinda like went after me," Fahrney said. "I kinda tried to defend myself, and the next thing I know I felt these taps on his side of my head, like, you know, like he was trying to punch me."
"I still didn't know what was going on until I felt something trickle down my chest, and I realized it was blood," he said.
At that time, a Winnebago County sheriff's deputy vehicle arrived.
"When he saw the cops he just took off," Fahrney said.
A deputy chased the assailant on foot and arrested him after a brief struggle, in which the deputy sustained cuts to his hands, according to Winnebago County State's Attorney J. Hanley.
MORE: What to know about the deadly Rockford, Illinois, stabbing spreeIn 20 minutes, four people were killed and seven injured in the rampage, authorities said. The victims included a mother and son who were stabbed to death at their home, a postal worker who died after being stabbed and run over by a truck driven by the attacker, and a 15-year-old girl who was beaten to death with an aluminum softball bat in her home, Hanley said.
Fahrney's neighbor, Lindsay Craig, was stabbed after the assailant broke into her home and attacked her with a knife inside and in the front yard, according to Hanley.
Hanley commended Fahrney's actions during a press briefing on Thursday for stopping to help Craig "without hesitation" by placing himself between her and her attacker.
Fahrney said he was just seeing how he could help.
"The cops were telling me, 'Thank you, thank you for getting this guy,' and I'm like, 'I didn't do nothing, I just, you know, I was just there to try to help,'" Fahrney said. "I had no idea what was going on."
The suspect, 22-year-old Christian Soto, was arrested and charged with four counts of murder and seven counts of attempted murder, as well as two counts of home invasion with a dangerous weapon, Hanley said. Soto remains in custody after his public defender requested that his detention hearing be postponed during his first court appearance on Thursday, according to Chicago ABC station WLS.
Following his arrest, Soto waived his Miranda rights to remain silent and told investigators he was high on marijuana he claimed was given to him by one of the slaying victims that he believed was laced with a strong narcotic, Hanley said.
But Hanley said Soto was conscious throughout the entire rampage and recalled details of each attack in his interview with investigators.
"I don't have a real answer for that," Hanley said of the possible motive. "And I'm not sure we will."
Recovering at home after the attack, Fahrney said he has eight staples in the back of his head where he was stabbed and a slash on his cheek but is otherwise "doing OK."
"I can't imagine what the other families are dealing with right now," he said. "I'm just happy that my son is safe, and my neighborhood is safe."
ABC News' Bill Hutchinson and Leah Sarnoff contributed to this report.
This story has been updated to correct the misspelling of Keith Fahrney's name.