A 24-year-old man was booked on suspicion of attempted murder Thursday after witnesses said they saw him douse a woman sleeping on a street bench outside a Van Nuys drug store with an accelerant before striking a match and lighting her on fire.

Witnesses told police that a man poured liquid -- possibly a beverage containing alcohol -- on the sleeping woman at about 1 a.m. outside a Walgreens store near Van Nuys Boulevard and Sherman Way. He lit a match and ran from the location, witnesses told police.

"I've seen arson deaths before, and it's very vicious," said Los Angeles Police Department Lt. Walt Teague. "We're hoping for the best."

The woman, who is in her 60s, was hospitalized in critical condition. The victim will likely be transported to a Sherman Oaks burn center for treatment, police said.

"It was like when you pour gasoline on something -- like an explosion," said witness Erickson Ipina, who added that he often saw the homeless woman in the neighborhood.

Friends told NBC4 they knew the victim as "Violet."

The man purchased the bottle containing alcohol in the Walgreens store, then poured the contents on the woman, Ipina told a Newsreel photographer. Ipina said he called 911 and followed the attacker, who brandished a knife.

"He told me, 'Stop following me, or I will cut you,'" Ipina said. "I kept following him and then the police came."

Police credited Ipina with helping to catch the suspect, identified as 24-year-old Dennis Petillo.

"He did a fantastic job," Teague said of Ipina's actions. "He was a good witness, he called police."