(CNN) -- Two additional homicide charges were announced Thursday against a suspected serial stabber who was trying to board an overseas flight when he was arrested, Michigan authorities said.
Elias Abuelazam is a suspect in 18 stabbings in three states. Five of the attacks were fatal -- all of those in Genesee County, Michigan, said the county's prosecutor, David Leyton. Four of the 18 attacks occurred in Ohio and Virginia. Abuelazam has been charged with homicide in three of the five deaths.
Earlier, defense attorney Edwar Zeineh told CNN that he expected "up to four new murder charges" to be announced Thursday. However, Leyton said Thursday that the remaining cases are still under investigation.
"There is a lot we have to comb through," the prosecutor said.
Previously, Abuelazam, 34, faced one murder count, five counts of assault with intent to commit murder and one charge of malicious destruction of property -- all related to attacks in Michigan.
The new charges stem from separate fatal stabbings of two Michigan men, one 43 and another 60. In the first case, a witness identified Abuelazam as the stabber after seeing his photo on television, Leyton said.
In the second, police obtained a search warrant for Abuelazam's luggage after he boarded a plane in Louisville, Kentucky, that was bound for Atlanta, Georgia. He was arrested August 11 at Hartsfield-Jackson Atlanta International Airport, where he was set to board a flight to Israel, police said.
Investigators found a pair of sneakers in his baggage with evidence of blood matching the DNA of the 60-year-old victim, Leyton said.
Abuelazam was indicted last week by a grand jury in Toledo, Ohio, in the stabbing of a church janitor.
Zeineh said he does not believe investigators have insurmountable proof against his client.
"I still feel strongly there is reasonable doubt based on my review of the evidence so far," he said, without mentioning specifics.
Abuelazam's mother recently flew from Israel to Flint, Michigan, to see her son, and has made several jailhouse visits.
"Her presence there as a mom was to empower her son," Zeineh said. "She helped him gather his thoughts and be [a] productive member of his defense team."
The three-state string of attacks began in May and ended in August. Most of the stabbing victims were African-American.
Federal officials have not provided a motive for the attacks. Leesburg, Virginia, Police Chief Joseph Price has said he believed the attacker was targeting African-Americans. Abuelazam is believed responsible for three attacks in Leesburg.
If convicted in Michigan, Abuelazam could face life in prison without parole. The state does not have the death penalty.
Authorities had Abuelazam in custody twice in a two-week stretch, both within hours of reports of stabbings, but he was released. Police said he had not been linked to the attacks at the time.
Abuelazam was arrested August 5 after a traffic stop and July 29 for allegedly providing alcohol to a minor. He was fined $125 in July. In the traffic stop arrest, in Arlington, Virginia, police arrested Abuelazam after learning he had an outstanding warrant for assault. A knife and hammer were found in his car.
Authorities now believe both weapons were used in the string of stabbings. One of the attacks took place in Virginia hours after Abuelazam was released.
CNN's Susan Candiotti contributed to this report.