FERGUSON, Mo. — No one is in custody and no arrests appear to be imminent, police said Friday as the investigation of who shot two officers at a protest in Ferguson continued through a second day.

Investigators are working around the clock, and substantial rewards have been offered, said Jon Belmar, chief of the St. Louis County police, at a news conference at department headquarters in Clayton.

A county officer, 41, was wounded in the shoulder and a Webster Groves officer, 32, in the face just after midnight Thursday while on a security line during a protest outside the Ferguson police station. Both were treated and released at Barnes-Jewish Hospital.

Three shots were heard, and believed to have been fired from about 125 yards away, to the northwest. Police called it an “ambush” and said it appeared that a handgun was used.

Belmar refused Friday to discuss any specific evidence or exactly from where the shots were fired. He said it was “a long way off,” but the target was a line of officers and hitting one did not require a “miracle shot.”

Responding to reporters’ questions, Belmar also said he does not know what motivated the attack.

“It doesn’t seem to be a coincidence that it happened there, that’s one thing,” he said.

He cautioned against being quick to draw conclusions, lest they lead in the wrong direction.

Various protest leaders have condemned the attack, insisting that violence was not the answer to discrimination against blacks in the community.

Wednesday night’s gathering came hours after an announcement that Ferguson Police Chief Thomas Jackson had resigned, effective March 19. Jackson had been a target of complaints since one of his officers, Darren Wilson, shot and killed Michael Brown, 18, in a street confrontation Aug. 9.

Last week, one Justice Department report said Wilson was justified while another strongly complained that the Ferguson police and municipal court combined to become a city revenue engine they preyed unfairly on the poor and blacks. The Justice Department is demanding reforms under threat of a civil lawsuit otherwise.

Protests continued peacefully Thursday night, with the county police and Missouri Highway taking over security command from Ferguson police.

About 9:30 a.m. Thursday, officers swarmed a home about four blocks from the shooting scene and questioned two men and a woman.

Belmar said Friday, “I don’t feel like at this point that is going to lead us anywhere.”

CrimeStoppers is offering a $10,000 reward for information leading to an arrest in the shooting; U.S. Reps. William Lacy Clay, D-Mo., and Emanuel Cleaver, D-Mo., added a $3,000 reward for information.