A 22-year-old man from Tulsa, Oklahoma, has been arrested in the shooting deaths of a Long Beach mother and her 4-year-old daughter as they returned home from grocery shopping, authorities said Monday.

Brandon Colbert was arrested Sunday after being matched to DNA submitted by detectives, Long Beach Police Chief Robert Luna said. Investigators believe Colbert boarded a Greyhound bus from Tulsa to Los Angeles three days before the shooting on Aug. 6. He had recently been arrested by the Los Angeles Police Department for allegedly stealing a vehicle.

No motive has been established, and Luna said the investigation remains active.

"We haven't ruled out the possibility that others may be involved in this horrific crime," Luna said.

Detectives urged anyone who had had contact with Colbert to contact authorities. A $40,000 reward previously offered for information leading to an arrest and conviction is still available, Luna said.

Carina Mancera, 26, and her daughter, Jennabel Anaya, had just parked their car and were walking back to their apartment with the child's father at about 10:20 p.m. when they were shot, police said. Mancera was pronounced dead the scene. Anaya was transported in critical condition to a hospital and died early the next morning. Mancera's boyfriend was also shot at but not injured.

The girl's father told investigators he did not recognize the shooter.

Detectives reviewed countless hours of surveillance video while forensic crime scene evidence was being processed, Luna said. In September, authorities announced they had identified a person of interest on a surveillance video from a local business. In early October, detectives upgraded that individual to a suspect in the case and said they were able to track him to the scene.

Police asked the public to help identify the man and followed up on every tip, but none led to a match, Luna said.

Then, on Oct. 31, the county crime lab notified detectives that the DNA recovered was positively linked to Colbert.

"An investigation of this magnitude that began with no leads is very difficult to work," Luna said. "Sometimes a case like this can take years to solve. So I'm extremely proud of our police department."

Colbert has been booked into jail. Police plan to present their case to Los Angeles County prosecutors on Tuesday.

It was not immediately clear whether Colbert had obtained an attorney. Reached by telephone Monday, Yolanda Colbert, who identified herself as the suspect's mother, said, "My son is innocent. That's all I want to say."