Police said dash-camera video from the cruiser shows the victims' Toyota Corolla had a red light when it reached the intersection and came to a complete stop just before the crash.
The officer from the Columbus suburb of Upper Arlington was responding to a reported armed robbery at a fast-food restaurant when the crash occurred around 1:30 a.m. at a large intersection with traffic lights, investigators said.
The cruiser was one of an unspecified number of police cars responding to the robbery, all with their lights on and sirens activated, said Upper Arlington police officer and spokeswoman Heather Galli.
A Columbus man was driving the other car, with his wife in the front passenger seat and four daughters, including a toddler, in the back seat, said Chief Robert Oppenheimer of Perry Township police. None was wearing a seatbelt, and the youngest daughter was not in a child restraint, he said.
"That car was just totaled, and they probably died instantly," Oppenheimer said.
Oppenheimer identified them as driver Eid Badi Shahad, 39; Entisar W. Hameed, 31; Shuaa Badi, 16; Amna Badi, 14; Ekbal Badi, 12; and Lina Badi, 2. Hamee and Shahad were married and the girls were their daughters, Majeda Mohammad, a case worker for Community Refugee and Immigration Services in Columbus, said Friday. The family were refugees from Basra, Iraq, who came to the United States about three years ago, Mohammad said.
Mohammad says the family had been out making visits as part of the Muslim holiday of Eid al-Adha. She said Shahad's mother and his four sons were home at the time of the accident.
The family lived in an apartment complex on the far west side of Columbus where most of their neighbors are immigrants from Somalia. A stream of visitors came by Friday to pay their respects. A service was planned at central Ohio's largest mosque Saturday.
"It's very sad, because this man, and this family, is excellent, excellent family," Mohammad said. She added: "He is a wonderful, wonderful man and wonderful family."
Franklin County coroner Jan Gorniak said an autopsy could be performed on Shahad as soon as Friday. She said autopsies won't be performed on the passengers because of religious objections.
A small shopping center sits on one side of the intersection, with a park and river on the other side. The intersection is frequently busy during the day, with hundreds of cars passing through it.
The officer, who had been traveling alone, was being treated for a serious head injury at a hospital but was in stable condition, said Jason Pappas, head of the local police union.
Upper Arlington police identified the officer as Shawn Paynter, who joined the department five years ago and had been on the overnight shift about a year.
Oppenheimer said the officer was in shock after learning about the deaths, and he had not been interviewed by investigators by midday Friday. That was expected to happen later with his attorney present.
Oppenheimer said a Columbus police accident investigation team pulled the dash-camera video from the cruiser. He said the footage shows the cruiser entering the intersection just as the light was turning from green to yellow.
The victims' car entered on a red light, Oppenheimer said, and then came to a complete stop in the middle of the intersection before it was hit.
"One could speculate that he may have realized he ran the red light and was going to back up," Oppenheimer said. "Or he saw the cruiser coming ... and he froze. We can only speculate, because we'll probably never know."
Associated Press writer Ann Sanner contributed to this report.