According to authorities, Ewell is responsible for three killings in Hawthorne and one in South Los Angeles. All four brutal murders happened in the span of about a month.
Ewell would pose as a utility worker to get into homes, according to investigators.
"If anybody has information that Ewell may have posed as such and tried to gain entry into their house, we'd like the public to contact either LAPD or the sheriff's department in their respective areas," said Lt. Dave Coleman of the Los Angeles County Sheriff's Department.
Officials have not said why Ewell went on such a violent spree. They said Ewell has been arrested before for burglary and armed robbery, but never for murder.
Ewell is accused of fatally attacking an 80-year-old man during a Sept. 24 home invasion in Hawthorne. Hanna Morcos was bound and gagged as his wife slept and later died of a heart attack that was partially blamed on the attack.
He is also charged with robbing and killing his neighbor, 53-year-old Denice Roberts, during an Oct. 13 home invasion.
Ewell is also believed to have killed Leamond Turnage, 69, and his wife Robyn, 57 in their Hawthorne home, just a few blocks from the Morcos residence, on Oct. 21. He allegedly bound, beat, gagged and strangled the couple.
Jewelry and electronics taken in the robberies were reportedly found in Ewell's home.
Authorities said Ewell was caught on surveillance footage trying to use the Turnages' stolen ATM card at a gas station on the day of the killings. He was arrested without incident two days later.
He was charged last week with four counts of murder and robbery. Prosecutors have not yet decided whether to seek the death penalty.
Anyone with information was urged to call the Los Angeles County Sheriff's Department at (323) 890-5500.
The Associated Press contributed to this report. Sonme of the evidence against Ewell includes surveillance video at a gas station. Authorities say he was using one of his victim's credit cards.